If you don't have a lot of good traffic obviously you will have little revenue.
Concentrate on the names with high traffic, first determine the origin of traffic: see if visitors are coming from backlinks for example, and check archive.org to see if the domain was previously developed. You can use google too (they may have a cache of the site). When you have a better idea of what visitors may be looking for then you can select more appropriate keywords.
Use the preview tools at Sedo so you will see what visitors get, if the ads are not relevant try different keywords. (That being said, I don't think that a name like pelargonium gets a lot of searches).