Checking out the tutorials here on dA is a good way to start! Look under "Resources" and try the galleries of =ClaireJones, ~CygX1, =JoelFaber, =MichaelFaber and also check out the *Apophysis club's list of resources. Keep playing & experimenting You might also like the forums here [link]
I see what you mean now! Mine are all one flame, but the way to get them to fill the frame is to use the "Master Scale" adjustment on the Render tab of the adjust window, In other words, you zoom in on them.