What are the best places for keywords?
keywords that can bring targeted traffic to your Web site and are often searched for, but still not so competitive as to make a top ranking

So, Want to drive trafic to your website? You should use proper keywords and place it in following locations:

HTML Title
Text of the page
Meta description
Meta keywords
ALT tags
Comment tags
URL name

Placing the keywords at proper place can drive more trafic to your site.