I started to blog in 2006, when I was just writing my first novel, JET SET DESOLATE, and hadn't gotten my MFA or published it yet. It was great that I started early, because now one can see the whole arc of my career on the blog as it all gradually happened.
When I first started blogging I was so excited about the possibility of sharing my thoughts on the Internet that I stayed home sick from my office job and set up my blog. This was back in the MySpace era.
I think it's a good idea to start early, while you're writing your first book. It will be very helpful later. It's a good habit to get into.