Avoid non relevant ads

If your blog talks about technology there is no reason to display ads about mortgage rates or hotels in Paris. Sure it might help you make some money on the short term, but over the long term it might harm your credibility since such non relevant ads offer no value for your readers.
Non relevant ads could include text link ads, sponsored reviews and direct sponsors. If someone is willing to advertise something on your site that is not even remotely related to your topic it means that he is just looking for the SEO part (i.e. Pagerank from Google). Secondly those ads might also discourage legit sponsors that do not want to get mixed with non relevant content.
I know it is hard to turn down potential revenue sources, specially when they help to pay your hosting bills. If you currently have non relevant ads or sponsors on your blog you could try to remove them gradually. Remove a single one initially and look for something else that could offer value for your readers.