Start by reading the Beginner's Digest, which is stickied at the top of the forum. Post any hands that gave you trouble and ask for advice.

Focus on putting your opponents on ranges for every street of play, even the hands that you are not playing. The better you get at that, the better your results will be.

Full ring is the best place to start if you want to play cash games. Short-handed tables have much higher variance and require stronger post-flop skills.