When stepping into a new promo environment (and this goes for boards, Yahoogroups, or whatever) take a few days to study how other people there do it. Check out what's going on in that particular community. Read some of the threads. Post on a few threads and let people get to know you before you start promoting. In short, don't just barge in like a bull in a china shop and start pushing your book in people's faces.
Example: As I said, there's a backlash on Amazon right now against indie authors overpromoting. There are of course as many opinions as there are posters (or possibly more), but the big problem for most people seems to essentially be 1. excessive promotion (bumping your thread too much and posting too many threads) and 2. mislabeling your thread so people click on it without realizing it's a promo. These are easy things to avoid doing, right?
Apparently not. Because a new author strolled into town this morning and posted a new promo thread with a title that doesn't indicate it's a promo. And now, not surprisingly, he's being told "go away, spammer!" Sigh. Never mind a few days; a few minutes spent perusing the busiest threads would have helped him avoid this error.
Subtlety is your friend, people!
ETA: To give the guy credit, he looked at the responses, realized his error, and deleted the post with apologies. That's good. Hopefully he's learned from this to look before he leaps in the future!