Avoid packing too many keywords into your keywords meta tag. The more words you use, the more diluted your really important words among them become.
The keyword tag in any page is best served by limiting the number of words to as few as possible. It is hard to say exactly at what threshold the search engines begin to "dilute" the effectiveness of keywords. It might be 10 or 5, or 7. If 3 is all you really need, limit it to 3.
There is a temptation to insert a hundred words into keyword tag section of your web page, and there might be pages out there that truly need to do that, but most web pages do not have such a broad reach. Use the body text of the page to contain all the words you are interested in supporting.