Start with the simple rhythm – rim-center-rim-(rest) – and work up in complexity. If you get lost, you can follow the "basic" rhythm of the atabaque, agogô, or reco-reco: 1-2-3-(rest), 1-2-3-(rest).
When you hit the rim, use the side of your thumb, as though you were flicking something off of your hand. When you hit the center, use your whole hand.
Did you know that you can change the tone of the rim hit? If you press the thumb of the hand holding the pandeiro against the instrument's skin, the rim hit has a higher tone; if you release that thumb, then the rim hit has a lower tone.
It can be useful to train yourself to play pandeiro with either hand; this way you can switch off if you start getting tired while playing.
Don't spank the pandeiro. Enough said.
Relax your hands and shoulders in order to get the best sound out of the instrument.
As with the pandeiro, the hit in the center of the atabaque should have a separate and distinct sound from the hits on the edge. The edge hits are deeper and hollower in tone; the center hit sounds higher and more "snappy."
Don't bang away carelessly on the atabaque! This instrument has the potential to be played very loudly, but in the capoeira bateria, it shouldn't be. Thus, take care that you're not overpowering the berimbaus with the atabaque.
The atabaque is the "heartbeat" of the roda. It must be consistent and solid in keeping the rhythm. In most angola rodas, variations on the atabque are discouraged.
It's best if the atabaque rhythm never stops: this means that when the person playing the atabaque switches off, the new player must come in and start playing without missing a beat.