A couple of people have asked me to expand on the techniques used to uncover explicit and tacit motivations. Let's start with explicit motivations.
As mentioned in the previous post, explicit motivations are those that consumers can tell you about directly. As such, the research to uncover them can be very direct. I'm not going to be prescriptive about specific research methods, because what's more important here is knowing when and how to utilize the information consumers give you.
If you are trying to improve your current offering, it is important to set up conditions in which the consumer can describe the actual use of your product for you. First, make sure to talk to people who are doing the task your product helps them to do. Then, make sure you talk to people who use your product, people who use your competitors' products, and people who do not use either. You want to understand the role your product plays for them. The same is true if you offer a service. It's important to set up use conditions that mimic actual use as closely as possible, and observe, as well as interview, the consumers. Most ergonomics and human factors research methods fall into this category. An in-context interview setting is often used, but if you have a group setting or online experience, that's fine also. Just make sure you are aware of the impact the method may have on the research.
Since you are trying to improve upon what already exists, you can take the consumers' comments at face value. The translation between what they say and what you need to do to improve is very straightforward, as the consumer is usually familiar with the existing category and offerings within it. You may not execute their specific suggestions, but the needs are discernable and solutions can be defined. Evaluation methods should be equally straightforward, and you may return to the same consumers for feedback on how well proposed solutions are working.
Direct research methods can yield great insights to the explicit motivations that drive consumers to use your product or service over your competitions'. Just remember that they are most useful in determining the best way to improve your offering, and are of limited value if used when you are trying to develop something that is truly breakthrough in your market.