My cousin is *really* good at chess, he plays against the top 50 ranked players in the world regularly. He started by just playing the game against anyone who would play him. When you play someone, don't just play the situation, but think about how that situation was created. Then go back afterwards and see if you can play out that same situation, and figure out what you could have done to put yourself in a better position.
Then, if if you really want to get to the "next level", you'll have to buy chess books and study openings and positions and have them completely memorized. That way, when you see them in a game, you'll know exactly what to do. You'll know what the weak points and strong points are of any setup or situation. This is really the part about chess that's boring -- simple memorization, repeating positions over and over and over again until you know all there is to know about it.
Most people can play a little, get a little better if they play more, but they tend to get 'stuck' at that level, they can't progress past that level of "decent" .....