Because keywords play such an important foundational role in the development of your search strategy, you will obviously want to spend a good deal of thought and effort developing a sound initial keyword profile. Keep in mind, though, your initial keyword research is merely a foundation. You'll work and rework your keyword profile throughout your campaign.
Developing your keyword list has several phases:
Collection: In the initial collection phase, you will simply collect large numbers of keywords and dump them on to a list.
Analysis: In the analysis phase, you will attach relative weight to terms and cull undesirable terms. For example, you'll undoubtedly collect terms for services and goods you don't sell. You'll obviously not want to put effort into ranking for such terms.
Expansion: The expansion phase will take place after your campaigns have been running for a while—this phase is a reaction to what you learn from the performance...