The keyword guidelines for our style of RSS link wheels are really no different than what you would expect for any other website or blog project. I generally like to target keywords (and keyword phrases) that get no less than 1,000 searches per month, and no more than 40,000-50,000 monthly searches. You can adjust these thresholds base on you marketing niche.
There is a vast amount of information about keyword research that you can find online. I will say that you do not have to invest in fancy tools and software. When I started online I decided I would use free tools as much as possible, and learn each step of the process until I became proficient. I now only use the Google Keyword Tool for my research. If you learn to do this right, you will know why.
Google is the only game in town that matters, so use Google and Google tools.
Here are a few more keyword guidelines I have found useful. Attempt to use keywords in URLs, titles, and subheads. A subset of this technique would be to use "keywords" for pages, categories, and tags.
This only makes sense, because everything online starts with keywords. Use keywords in your headlines and throughout your posts and articles. At the same time, don't keyword stuff, as this will result in being penalized by the search engines.