Our board has been up for 9 years and we have had ads for about 6 of those. Here are some seldom mentioned considerations.
Snowballing - Make rates affordable enough to where you get multiple advertisers and they stick around. Email their competitors about advertising opportunities on your site. The more advertisers the more people will feel left out who aren't. It doesn't make sense to have a 3x$ rate if you only have one advertiser and they drop after 6 months. In my mind having 3 at 1x$ is better.
Run Ad Software - Use OpenX and give them statistics. Make sure they understand that CTR is usually in the 0.25% range. If they are running Analytics they will be able to track their clicks and conversions.
Don't drown your visitors - Sites typically use too many ads. I'm not a huge fan of 1st post ads, maybe for unregistered visitors, but not for registered. We have daily visitors from people who have been with us since day one and their contributions have made the site it is today. Don't punish them with a bunch of irrelevant ads. I would say if you are not making over $100/month from AdWords keep them to a bare minimum.
AdWord Insanity - Having too many AdWords ads can actually drive down the keyword rates for you site and you will actually make less. I think there is a post about this on W Revenue somewhere (Scott from PhotoPost). It's simple econ really, if supply outstrips demand your price will go down.
