It would depend on the title of your hub as to what key words to use.
Always place the title of your hub in to the content you are writing, (remember it has to flow with the content)
A tip i always use, is to find similar hub pages, articles, and blogs on the subject subject i am writing about to see how they may be placing key words.
There are a lot more tips i suggest typing your question in to google hope this helps. :)