When one goes about explosions, another way to think about approaching it is breaking it down into layers.
I do explosions this way now; think about what you need to animate and assign a layer to each.
First, I roughly sketch the form expanding and the particles coming out, and get the timing to what I want it to be. After that is to where you want it to be, try using different layers. One for smoke, one for firey bits, some for particles and then another for debris. I did this real fast and shitty but you get the point: Example.
For this, you can see how the animation is broken on to layers. Fire, smoke, debris. HERE
(the animation is awry, as its a bit old, but it should get the point across).
Also, slightly related and in addition to this kind of explosion, think about how you could imply an explosion through lighting. Here is another bit I did a while ago that emphasizes explosion without actually animating the explosion- just through lighting the illusion is given: HURRR