One of the most important things is playing in a group, letting people know that you exist and you are a musician. You can't do this right from the very beginning, you have to acquire a certain level first. The moment you feel you can play, gather your friends that study music and convince them to play together.
The members of the group will bring their own instruments. You already invested time and energy studying and practicing so you should also invest some money to make the group sound as well as possible.
Maybe you won't find a genius fellow musician that will agree to play with you in the beginning but it's necessary that at least one of the fellows in your group will be a decent musician. Any group, at any stage, must improve and the only one who can take it to the next level is a good musician.
Years passed by and you made a name for yourself. Now you can choose. Pick those musicians that play a music that intrigues your ears. Think what instruments and what voices will fit your project.
It's not enough for a group member to be a good musician. He/she must also share your vision, your ambitions and, most of all, be an agreeable person. You'll spend a lot of time with those mates and, if there's no understanding, life will be hell and the group will soon disassemble.
There will be also a member of the group who is not a musician: a promoter or a manager. Usually, he/she is the nicest person around. But what really matters: does he/she do his/her job as it should? Does he/she get enough gigs for you? Does he/she fight for you? Is he/she ambitious enough?