I recommend approaching a CRM deployment project like a modern development project - use Agile and Iterative methods.  Taking an agile and iterative process will ensure that you deliver business value early, respond quickly to change and feedback, ensures that users are involved in the project, and results in the highest satisfaction at all business levels.

I recommend reading The Principals of Agile Development before you plan your CRM implementation project.  It is a quick read with only 12 statements.  Although the Agile Manifesto was written for the software development process, it is completely appropriate for any large scale software deployment, and especially important for CRM projects as they have a traditionally high rate of failure using waterfall approaches.

I think the most fundamental indicator of whether a CRM project is going to be successful in an organization is a solid understanding of their business models and the consistency of which those are applied.  It is not necessary that these processes be written down prior to starting the CRM project, it is just that they have to be known and understood by everyone in the organization that interacts with customers or partners.

When embarking on a CRM project, it is important to start by identifying (and preferably documenting) the existing business processes.  I would recommend starting with pre-sales processes, sales fulfillment processes, then moving into customer service processes.  This is the primary revenue pipeline of most organizations that sell goods or services and it is important to understand all the processes that are involved in this pipeline.  Marketing activities and processes can be modeled in parallel as they are not directly involved in the revenue pipeline, but they are required in order to bring new leads to the organization and also encourage continued revenue from existing customers.

Flowcharts are excellent tools to document business processes for discussion and review by all key staff in the CRM project.

It is recommended that the existing processes be documented, even if they are wrong, before starting to document any end-state process.

When planning your CRM project, try to take an approach that minimizes process changes early on in the project.  Process changes are very expensive for most organizations and require that all staff support the change and actually change their behavior.  CRM projects that rely on early process changes are at a significantly higher risk of failure because of the costs and risks involved in implementing process changes prior to the organization realizing business value from the CRM and having full organizational acceptance of the CRM.

Many successful CRM projects are implemented using a series of small and incremental pilot projects.  This means selecting small teams of individuals with a limited scope, implementing for them, then extending the solution to larger teams and more processes.  It is common for organizations to start by implementing the CRM as a glorified contact manager starting in their sales team.  This is usually done because there is low effort required to implement the CRM in this fashion, there is a high business value to the sales team, and it is easy to increase operational awareness of the sales process in the organization and therefore good buy-in at all levels of an organization.  This approach also ensures that the CRM gets populated with a substantial number of active and relevant contacts.

Selecting a small initial pilot is important.  If you have a larger organization, don't start with the entire sales force - start with a smaller team responsible for a single region or country, or with a team responsible for a single product.

Once you get a successful pilot and find that the pilot users are spreading the news of the successful pilot and the real benefits that they are receiving, then expand the project in incremental stages.  You might consider extending to the remaining sales teams, across all product lines, and once sales is implemented perhaps move into customer service areas.  There is no defined prescription of the order, just that you should be selecting the pilots in the order that makes sense for the project to succeed in the organization.  Try to implement earlier where users will receive significant value from the CRM project before tackling areas that will require massive amounts of process changes without benefiting themselves.

The CRM application may be software, which makes it a technical project, it is imperative that the project consider the human factor.  Most efforts in implementing a successful CRM project are not technical.  A CRM project will change people's environments by introducing process changes, new reporting requirements, visibility of the individual's performance through a larger audience, and it can also hit their pocketbook as customer data becomes more visible and usable by others in the organization, threatening any existing little empires that are built.  Just remember, people don't like change, so the only real way to succeed is to do it with their cooperation and support, and that means identifying and delivering significant value to the individual and not just the organization as a whole.

CRM projects get deployed into existing organizations.  There is a high probability that an organization will have a significant amount of data collected on leads, customers, and transactions.  CRM systems have import tools and it is very tempting to import as much data as possible into the CRM.  If this is not carefully considered, it could easily sink the project.

Data quality and relevance must be top of mind before importing anything into the CRM.  The easiest way to sink a CRM project is to import stale or out of date information that is no longer accurate.  For example, importing all leads from all trade shows ever attended will likely fill the CRM with old leads that do not want to be contacted and probably with old contact details that would be inefficient for an organization to follow up on.  Cleaning that data once it is in the CRM is an expensive operation.  That said, the most detrimental effect is that the information that your users will be working with on a daily basis will get lost in a sea of old leads or contacts.

It is recommended that an organization carefully plan the data lifecycle and management responsibilities for all data that is designed to be input or imported into the CRM.  For example, who is responsible for validating and maintaining accurate customer phone numbers and addresses?  What criteria will be used for pruning stale data once it is input?

Spreadsheets are great tools, but they have no inherent workflow capabilities on their own.  A CRM system is an operational database that has a strong workflow model.  Significant business value can be received from a CRM deployment by implementing tasks and notifications using the CRM workflow mechanisms.  Users will benefit from higher efficiency and job satisfaction if they can trust the CRM workflows are tracking their relevant tasks and that they are getting notified consistently for all key events.  When you are designing your workflows, consider the workflows that will increase the efficiencies of the users, help them not miss important steps in the process, and ensure that everyone is properly notified of all key events in the process.

CRM systems have excellent reporting mechanisms.  The reporting mechanisms of a CRM should be used at all levels.  The organizational leaders should have key performance indicator (KPI) reports so that they can manage the organization and financials as a whole, the sales directors and managers need good summary reports to show sales activities, key clients, new opportunities, and more.  Finally, even the lowest users in the system need reports that help them ensure that no leads are neglected and that all processes are followed in a timely manner.  CRM reporting mechanisms help increase the visibility of the organizational processes, customers, and events in a manner that does not require a lot of human intervention or effort to implement on a regular basis.

When you are implementing the CRM in your pilot projects, try to deliver reports that span all the levels of the organization that are related to the pilot team.  For example, if your pilot team is a sales team in a region or office, prepare the KPI reports for upper management, the regional director, the office manager, as well as for the individual sales representatives.  This will ensure that the visibility of the project will remain high and that the business benefits will be delivered early in the project. 

Adding custom attributes to contact records is a very easy thing in the CRM.  It is a frequent mistake to over-design a CRM by adding too many attributes, and specifically too many required fields to a contact record.  Please consider that people have to use the form and if it is too difficult or takes too long to fill in the contact forms, people will stop using the forms. 

Each data field that is added to the CRM will need to be entered in all the records and the information reviewed and maintained until the field or records are deleted.  Adding fields that are seldomly used makes reporting useless and only serves to crowd the user interfaces with fields that are not used.

The best advice is to use the KISS principal:  keep-it-simple-stupid.  Only add fields as they are needed, and only if they are needed.  Double check that mandatory fields are truly mandatory.

It is pretty easy to identify the other big systems that need to be integrated with the CRM like the accounting system, but it is much more difficult to find all the other sources of data.  I do have one tip though - look for any Access database or Excel Spreadsheet that is used by your sales team.  These spreadsheets and micro-databases are typically the life-blood of the sales team.  It is important to find those spreadsheets as early in the process as you can.  The spreadsheets are extremely useful tools to use to reverse-engineer to identify key processes that might not have been identified through interview techniques.

One of the advantage of spreadsheets is that that they are typically fairly easy to model in the CRM, and moving the data to the CRM allows users to work better as teams, with no more file locking issues and new reporting and workflow capabilities.  That said, be prepared for a fight to relinquish the use of the spreadsheets.  People will hold on to them dearly, especially if it is tracking data that is absolutely useful to them to perform adequately on the job.  You might consider tolerating double entry for a while, staying in constant contact with the user, and helping them to feel confident in the new system.  A good sign that the system has been designed properly is that they voluntarily drop the use of their old spreadsheets.

Also keep in mind that it is more important to ensure that the organizational processes are being followed and that the data is accurate than to try to reduce the costs of double entry.

A CRM system is an operational system that should evolve and adopt in step with your organization.  It is very important to not pitch the CRM as a finite project and only resource the project team members on a temporary basis.  The CRM will require ongoing maintenance and customization.  Permanent responsibilities and ongoing user training for new staff should be considered up front in the project.