Basically what these guys have been saying...just practice and improve. Double check grammar. Make it a reasonable length, and don't do script version; it's such a cheap way of producing a story. Example:
Godzilla: *roars and fires an atomic blast*
Mothra: *cries out and dodges*
Godzilla: *roars and bites leg*
Mothra: *cries out and begins flapping wings*
While this could possibly work for a movie scene (with A LOT more detail added) it just doesn't suffice for reading. Now look at what it could be turned into if written as a proper story:
Godzilla glared at the giant moth godess before him, her wings containing multiple colors, causing a slight breeze every time they moved downwards. The mutant lizard roared out in disgust at Mothra before firing his atomic ray, energy seemingly pulsating from the blue beam.
Mothra, quite alarmed, let out a chirp as the ray quickly approached her before swiftly descending below its range. Enraged, Godzilla aborted his current assault before roaring out again in pure rage. Before Mothra could react, the monster king bit down on one of her many legs, cries of pain emitting from her mandibles. Re-focusing, Mothra began to flap her wings, releasing golden scales into the air. Godzilla tried to ignore the poisonous scales as they filled his throat, but to no avail; the demonic lizard let go and cried out once more as Mothra began to create more distance between the two.
As you can see, this make a much more interesting read. While I didn't state exactly where the battle was taking place, or at what time, it gives the reader enough information to create a mental image.