1} You must allow us to advert there. If we try to link back and can't, your ad will be deleted.
2} Your ad must not be profane in any way, nor graphic or sexual. PG-13. If your site isn't then just avoid making your advertisement match the site.
3} Be polite and courteous. For example, no spamming, or advertising by PM. Get reported and things will not go well.
4} You may advertise 1 time per 3 weeks per site. Though I prefer that you bump it. Mistakes are understandable, spam isn't.