There are three things that determine "good":
- Breadth of knowledge
- Pocketing skills
- Positioning skills
Knowledge is gained from experience (this assumes you are paying attention to your mistakes - and the mistakes of others). You learn the most from losing, and the least from winning. To gain knowledge, when you experience a loss, figure out what the causes were - and practice the skills needed and make mental adjustments to your playing style. That is what will improve your chances of success. Whether we like it or not, failure is what sharpens the mind. Keep in mind that nothing can be learned from success, except that you become a little too arrogant and there are a lot of people who will be happy to trim your pride.
You can also learn by watching other players' successes and mistakes. Recognize the playing errors of others, and you can more clearly see your own. The various instruction books, videos, and internet resources can provide a quick way to gather knowledge. The best way to improve is with an instructor.
Pocketing skills are necessary. When you first start playing, making balls fall into the holes is your absolute first priority. There are such a variety of ways to make the balls go in, that this effort will take some considerable time.
Positioning skills is the last general area that needs to be learned. This means working out the mysteries of controlled cue ball speed and spin. As you work your way through the various ways to do this, your skills will improve. It becomes a lot easier to make a target ball if you move the cue ball to a position that makes it an easy shot.
Your definition of "good" will change dramatically as you expand your knowledge of what it really takes in skill and abilities. As you improve yourself, you move up in the local competitive hierarchy. Remember also that as you get better, your lesser skilled pool player buddies will be unable to accompany you. Your skill level determine the size of the pond you play in.