As a fairly new player myself, I've asked this question quite a few times to different people. Most of what I've gathered from a combination of advice and reading strategy articles is this:
-- Position seems to be one of the most fundamental concepts in the game, regardless of who you ask. In each and every hand I think this is the first thing you should think about, before even considering what your hand is.
-- Starting hand strength relative to position is the next step, and a big part of this I've realized is understanding that there are a lot of deceptive hands that you might think are good, but should often fold. i.e.
in early position.
-- Bet sizing and playing around your stack size. I've noticed a lot of other beginners I play with at house games seem to just make random bets and don't pay attention to the size of the pot, or their own stack. Most people will insist that if you are below 20 BB you need to shove or fold.
-- Understanding the simple mathematical concepts. Initially I was reluctant to try to get into the math of poker because it seemed daunting, but things like counting outs and calculating rough pot
odds are actually very easy once you learn to do them.
Hope this helps!