You could leave it like that now. But the shine effect depends on the black/white in the alpha channel.
Darker = stronger effect
White = No effect at all
I find that its to dark in my channel, to adjust that I go to Image=>Levels.
You'll get this new window. In there you can play around with these sliders to alter the contrast between black/white.
I dragged back the white to the middle make it stronger.
Just play around with it to see its effects on the channel, once your happy just hit OK.
Thats it for these first few tips.