The sound of a metal agogô is high and sharp enough to be heard over all the other instruments, so STAY ON BEAT! If you have trouble staying on beat, follow the 1-2-3-(rest) of the atabaque, the pandeiro, and the reco-reco.
Some groups play low-high-low and others play high-low-high on the agogô... you'll have to ask your particular instructor which way your group does it.
You can improvise on the agogô, just make sure you stay in the general rhythmic structure.
The reco-reco is a pretty simple instrument and a good one to start out with if the idea of playing instruments intimidates you. The rhythm is the simple 1-2-3-(rest).
Turn the open end of the reco-reco away from you, towards the roda.
You don't make all three scrapes in the same direction. I usually scrape away from my body on 1, towards on 2, and away on 3; this seems to be most natural and flows the best.
One variation for the reco-reco is 1-2-3-4-5---6---