Make time to write. Especially the busier your life gets — you keep making excuses and keep promising yourself that you'll get around to it. Sometimes setting aside a specific time and then stapling yourself to a chair and writing is the best thing for your own improvement.
That, and of course knowing the rules of spelling and grammar (and yes, there are rules) is invaluable.
"He yanked himself free and fled to the kitchen where something huddled against the flooded windowpanes. It sighed and wept and tapped continually, and suddenly he was outside, staring in, the rain beating, the wind chilling him, and all the candle darkness inside lost."
The grand in the hotel rings with broken tunes; the guests frown; the concierge winces. But the blue-hatted boy is happy and braver than they. — TheMythMaster
