Hello!
I have 3 blogs that cover a very wide range of ideas/contents. One is for marketing, one for Fractional Investing, and another is a fun site. There seem to be two things you really need to think about when placing ads on your blogs. 1. What is your target audience? 2. Where is the ad placed ?
Don't place you ad in a general posting area, place it in a side bar. Make sure that if you allow comments, you have moderated ones. The reason for this is that there are some auto blog posting services that place comments that are actually an ad that can conflict/compete with YOUR ads!
Remeber, many blog services have the capability of you to have Google AdSense blocks on your blog. This is another way for residual (very small) income from people just clicking on the block ads on your blog. Remeber to select the words not to have content bots use so you don't end up with competitors on on blog.
Dave