I'm looking into this now as I'm starting up a new blog soon as I have been saying for months which I'm hoping to monetise, I just don't know how to.
I've googled it a bit and have discovered that supposedly, the best two options are Google Adsense and Amazon Affliates/Associates. I have found ways to do this easily on blogger, but I've recently switched to wordpress and can't find as much info on that that makes sense to me (I'm still getting used to it). I have seen things which suggest that monetising on wordpress is more difficult though but no exoplanation as to why.
I also want to focus my personal blog a bit more for future monetising purposes, does that kind of thing work? I have a generic blog and I'd like to focus on knitting, a knit-based business I'm setting up and chronic pain/diagnosis process. I could use categories to easily separate these but should I just have a separate blog for each? I still want it to be personal too so there will be other bits thrown in.
I'm not after a fortune, a couple of quid extra a month would be nice if the blog is going to be there anyway though! I'm hoping that they will end up paying for themselves wrt paying for the domain name essentially.