Make landing pages that don't look like landing pages. Don't cloak, redirect, or stuff keywords. Use proper html/css (no font tags, gif table hacks, and other crap that belongs in 1996), have a privacy policy and TOS, a few outbound links to real sites, and make it natural. This is not only good for quality score but for potential users. People like sites, but not so much landing pages. Hope that helps...
Here are some tips on improving your quality score. Just remember it's all about revelance. Good luck.