Most paid search professionals recommend keeping between ten and twenty keywords per ad group, and those keywords should all be closely related to one another. The reason is that your ad copy needs to match what the keywords are about. If you put too many unrelated keywords in one group, your ads become generic and stop connecting with what the person actually typed. Fewer, more focused keywords mean your ads feel more relevant and get better results. What number of keywords do you personally find works best in your campaigns?