Volume boosting shampoos always help. I don't know what is available to you where you live, but I always found Dove to be very good.
Hairysprays and gels can come in handy too - make sure you don't overuse them though, they can damage your hair.

After washing your hair, stick your head upside down and blow dry it. Spray some hairspray while your head is down too, it gives it volume from underneath.
Backcombing is also good for increasing size. Don't use a thin toothed comb for it, though.

I don't know much about afros, but I'm sure the same rules still apply to the other hair I've styled.