It's perhaps a bit early for this, but here's what I think I have learned in the past few weeks of advertising through Project Wonderful:
- Advertise outside your immediate niche: The most effective ads I've taken out were ads on popular webcomics such as Saturday Morning Breakfast Cereal or Questionable Content. These popular general-interest comics probably have more fantasy fans among their reader base than most individual genre fantasy comics have fans.
- Go for the pageviews. When you bid on an ad, pay close attention to how many pageviews it has. Pageviews are a pretty good indicator of how many clicks you will get.
- Notwithstanding the above, ads on ComicSpace are hugely overpriced (average bid value $7.2 at the time of writing). Don't bid on them until their price drops to, say, a tenth of what it is now. Hype and fads can add value to an ad; in ComicSpace's case, one could argue that the ads are seen by rabid comic fans who are not yet webcomics fans. In practice, though, I've got fewer clicks out of these than other popular webcomics sites or even genre niche sites.
- Do bid on ads within your niche if they are cheap.
- Skyscraper ads are worth it.
- Novelty ads may or may not be worth it (ask Jeff Rowland) but they're going to cost you.
- Generally, if you want an ad to stay up, overbid.You may end up having to pay prices similar to those of a traditional ad slot on a similar site.
- If you bid on multiple ads within the same block, and only one bid is accepted, cancel the ads that didn't make it after a day or so. Otherwise, they might become the highest bidder after a while, costing you unnecessary money. Double ads add no value. Also, from an ethical point of view, leaving the losing bids up amounts to giving the ad's host a free gift of someone else's money. By the way, if you want to give an ad host a free gift of someone else's money, it's usually possible to guess how high you can bid on a button ad within a block and still lose. This could turn out to be a weakness in the PW system. Don't abuse it.
- This may be a browser-specific thing (I tried in Opera and Safari) but it looks like the "edit this bid" feature doesn't do anything useful except cancel a bid. You can't alter the value of a bid, so if you must have an ad on a certain spot, you must bid again. If you bid repeatedly on the same ad, make sure to cancel the losing bids. Otherwise, when the bidder or bidders who caused you to lose the bids cancel theirs (or their bids expire), you may end up bidding against yourself and throwing money away. This has happened to me.
That's it for now. I may add a few more items if I think of any. Or I may not. All of the above is based only on my own experiences, is completely unscientific and may be wrong. Seems to be working for me though.