There are several ways to string a berimbau. It's easiest to get someone to show you the first time. Don't be discouraged if you have a hard time with it; it takes strength and practice!
One way involves placing your knee against the middle of the verga, putting weight on it while pulling back on the top of the verga to bend it, then wrapping the wire around the top.
I'm too uncoordinated to string the berimbau by the method above, so I prefer to place the bottom of the verga in front of my left ankle, step over it with my right leg, and bend the berimbau around the back of my right thigh. I pull the top of the verga with my left hand while wrapping the wire around with my right.
The cabaça should not be much higher than one hand-span above the bottom of the berimbau. Squeeze the wire while you slide the cabaça on.
Always unstring the berimbau when you're not using it. Your berimbau will last longer!
Half the battle is holding and balancing the instrument... but all it takes is (a lot of) practice! Try a few exercises: holding the berimbau and moving it back and forth towards and away from your body, left and right, as well as tilting it side to side and forward and back, while attempting to maintain control.
Don't be surprised if your pinky finger hurts and even goes numb for a couple days. It's normal, it'll go away, and with more practice your endurance will improve.
There are three basic tones on the berimbau: the high tone (played with the dobrão pressed against the arame), the low tone (played with the dobrão not touching the arame), and the buzz tone (played with the dobrão touching the arame lightly). Each type of tone should be clean and distinct.
Practice, practice, practice the buzz tone! Most people have trouble with it.
Make sure to hit the arame above the dobrão for the high tone and buzz tone, and below the dobrão for the low tone.
RELAX your shoulders and your hand while playing! It will help you get a better, louder sound.
The berimbau is usually held away from your body when you play either the low or high tones, and against your body (cabaça pressed against your stomach) for the buzz tone. This helps you get a nice, resonant sound.
Make sure to hit the arame with the baqueta straight on, and not at an upward or downward angle.
Most of the impulse for moving the baqueta comes from your wrist - not your arm. If you move your arm a lot when you play, you'll have a very hard time when it comes to rhythms and variations.
Relax your hand and let the baqueta bounce off the arame naturally. Don't hit and then pull the baqueta away.
In angola rodas, each berimbau has a specific role. The gunga sets the main toque: let's say it's playing angola (tch tch dom dim). The médio will invert the toque and play São Bento Pequeno (tch tch dim dom) and the viola will improvise.