that is i am supposed to choose keywords for a half regular site half blog web and it does not have any topic uniformity. Each post may be about a complete different topic. And if i choose site keywords that dont fit with individual articles keywords and content i risk being penalized. What should i do. For the moment iam only reading about it. There is no work done yet.
Then just skip the keyword research part. Dont choose any keywords. The search engine will index your site and determine your keywords using rank scoring algorithm. Thats what its job is. For example. Word1 -> Importance factor x, Used n times Word2 -> Importance factor x, Used n times and so on.. Its going to work like a word frequency counter. So just skip the part about choosing keywords to focus upona nd let the seaerch engine do the worrying for you.
Search the keywords that related to main topic of your post, try to write naturally regardless of repetation of keywords.