Fireballs are really easy but it's best if you have a WACOM tablet so you can take advantage of its pressure sensitive features.

Step 1: make a ball

Make a white ball on it's own layer...easy

Step 2: Make a glow

I don't use Layer effects for this. I make a copy of the ball. Select it...expand the selection by 5 pixels..feather the selection by 5 pixels and fill it with orange or a good fire color.

I then merge the original white ball onto the orange glow I created...should look like this.

Step 3: Get to smudgin'!

I start with a larger brush setting and softly drag from the center out. I then choose a smaller brush setting and make the little wisps you see around the edges. If this was blue it would make a nice Plasma ball. The Wacom tablet allows me to control where the wisps fade out. If you don't have a wacom tablet you may have to go back in with the eraser tool and taper off the wisps manually. If you smear the ball in one direction only you can add the illusion of motion.
Give it a try!