Marketing, sales and customer service are the three key functions of any CRM software. Realizing this will make choosing the right CRM app easier because by looking at the three components of CRM software you'll know what needs to be covered. Some CRM software only focuses on one aspect of customer relationship management, like sales, and you want a system that focuses on all three. The only way to apply customer relationship management correctly is to find a system the encompasses all three key functions.

Marketing -- CRM software should generate sales leads, manage leads, verify leads, and hel
run marketing campaigns in all your marketing channels, tracking every move made by every department, along the way.
Sales -- This feature in the CRM should help sales professionals be organized in their sales strategy by organizing all the data appropriately. You should be able to deal with everything including: Prospects, RFPs, qualifications, quotes, budget, spending, products, closing, (or losses) dates, milestones and more. The system should guide representatives to carry out all these activities in a streamlined, efficient and organized manner.
Customer Service -- This can be anything to do with servicing warranties, to handling service agreements, to planned and unplanned ticket management and call center support.

After that, ensure that your CRM app:

Is cloud-based -- By choosing a cloud-based CRM application your contractors and employees will be able to access the system from any location with multiple devices allowing for time and place flexibility that an onsite system will not. If you and your staff aren't limited, then your CRM can be better than ever before.
Offers free upgrades -- If you're paying a monthly fee for your CRM application then it should offer free upgrades whenever they have an upgrade. This way, your software is always up to date with the best security and features your money can buy.
Is flexible in size -- Ensure that the space you use can be upgraded or even downgraded depending upon what you need. For instance, if you only have 5 sales people right now, why should you have to pay for 50? If you only have 1000 clients, why do you need to pay for
10,000. If the system is seamlessly flexible in terms of the space you use and the features you want, then you can change your needs on the fly without having to find an entirely new system.
Integrates social media -- Today, social media is more important to your customer relationship management strategy than ever before, so make sure that the app you choose integrates with the most popular social media for ease.
Offers training -- Instead of having to spend your time creating training for the product, ensure that the product offers training to your staff for you. The training can and should be in both PDF and video so that your staff can become knowledgeable about the system in their own time and space.
Is user-friendly -- Most cloud-based CRM apps offer free trails so that you can test out the system yourself. Ensure that every department tries out the system's features important to their department and reports back their thoughts. You may need to try several apps before everyone comes to consensus about which app is best for your business.
Generates reports -- Metrics are an important way that any business decides if what they're doing is working. By having easy to generate reports, all departments can analyze what is working and what is not working, thus improving steps and systems along the way.

Finally, there is a lot of complimentary information to be had that is created by experts on CRM and CRM apps. GetApp.com, along with several industry professionals has produced a free educational eBook called: "Powerful Customer Relationship Management For Small Business." No need to give an email address to get it.