When you start to get serious, and begin to aspire to make money from blogging, you cannot do enough research.

When I was completely new all I wanted to do was to get a blog or site up and running, I didn't even bother to check how profitable the topic or the niche was.
I didn't take into account the competition or if there were any affiliate products for my niche or what method other sites in that niche were using to market products or attract traffic.

Its always good to know what your in for, before you jump in the deep end.
Potentially you will be investing a lot of your time into a blog in order to make it successful as quickly as inhumanely possible.
Having performed thorough research will let you know what your in for before you make any commitments.

I realize that for many people new to blogging and internet marketing just getting something up online is their top priority.

But from learning the hard way, really nothing is more satisfying than performing really good, thorough market research and having your site break onto the first page of Google's search results within four weeks.

Because its when you do this, that you know that your doing a lot of things right, from the very start to the end where your on top of your niche.

The only other thing I would tell a newbie is learn, learn, learn.
You really have to get out there and research and try and find out.....

"What you don't know!"

Because it goes without saying, its what you don't know which is preventing you from becoming successful.
You really have to be an 'Information Sponge' and soak up as much as your grey matter will cope with!

(Thank you very much for your comment on my CP, does that mean I get a job?... Kidding)