Hey, I'm having what I'll call moderate success marketing a blog with multiple topics but I can't really know how well it's going until I have other sites to compare it to so.... If you run a blog that is about multiple subjects I'd love to take a look. I'm finding that I 'm having the best results when I don't jump around too often meaning it works best when I write 10 photography posts in a row followed by 10 social media posts and then 10 psts of another different topic. I switch the advertising to reflect the topic I'm posting 10 in a row on too, ie: if I'm on a photography roll I promote shopzilla cameras for example. It seems to be working well and individual pages are fairing well in google so far despite the entire site not being 100% about one topic.
Why dont you categorize your posts and then run relevant ads for each category? This way you dont have to change your ads every now and then. Just my 2c
its good to have one theme blog but if you have wide knowledge of various fields then you can create mulitple topic but categories it correctly. Now about promoting you blog will be much difficult because you have various keywords so if you are targeting specific keywords then its difficult or you can target catergory wise rather than post wise
I agree with reliable1 simply add separate categories in the side bar of your blog, and add ad's to suit each theme.