adwords is a science. largest mistake anyone could ever make is launch a campaign and go right for the most expensive cpc, use the tools provided by google. so often are they over looked. use the google keyword suggestor and sort by competiton and build from there. Keywords with low comp. will usually convert good, build from there and then jump into the more expensive keywords.
also, dont be afraid of content targeting. if someone is working hard to get there website number one organically and you notice that they offer adsense, then by all means advertise on the website. it will make for a good return and save you money via the regular search results.
always split content targeting campaigns.
NEVER USE BROAD SEARCH - broad search = flood of crap traffic and low conversions.
dont be affraid to mimic the top competition - do not copy, but mimic. if your playing with an expensive cpc and they are up every day then they must be doing something right.
know your market - the ability to run ads on a time schedule is your friend. know who you are targeting and when they surf. - imo saturday is crap, my conversions are always low on saturday as they are for almost everyone, so why risk the money?
anything in here or another topic you want me to blab on?