Find Somebody To Play With

It is very important that you have someone to jam with or someone to assist you. If you're a beginner you should team up with somebody better than you as it will be easer for you to play with such a person because they have more control and experience so even if you mess up on the timing or something of that sort, they will slow down and wait for you. It is a great way to improve your musicianship and understanding of other players. There isn't a better feeling than that when you are playing with someone you know very well and you completely understand each other and can both change the speed at the same time. There is just something about knowing the person for a long time that creates a bond between you that will allows you to communicate without actually speaking.

If you are more advanced you might want to consider forming a band. It would be a good experience to play with real people instead of a backing track. Make sure they are about the same level as you are, because you don't want someone to be a lot better than everyone else and wanting to play songs that are impossible for you to play at that stage. Also you've got to like the people you play with. You will spend many hours with them and the last thing you want is someone annoying being there. Playing with a band would definitely improve your timing. When you begin covering songs start with backing tracks and then try playing just by yourself and see hoe you sound there will always be something to improve on. Find people that are into the same type of music as you are, because you don't want to have to learn a song you don't like and wont enjoy playing. 

If you're advanced and have time you could help out someone who is not as good as you and teach them a few things. Teaching is good as it forces you to analyze your playing style and techniques which cause you to find out a lot about yourself. This can sometimes be very helpful, for example when you find that on a certain riff you should start on an upstroke instead of a downstroke.