Get used to writing good headings
No, not just good headings - brilliant, witty, eye-catching headlines. Funny, poignant, memorable headings. Use the tabloids for inspiration. Or a carefully managed swipe file.
Swipe file (see above)
It's not stealing, it's a legitimate process - learning from what has been successful in the past. If that means ads from the 1940's then that's fine. If it's modifying web copy you saw a few weeks ago that's fine too. But there's a thin line between adapting working designs or copy to your own ends and plagiarism. People don't take kindly to being mugged.
Short, pithy sentences
Cut out the long sentences. Anything over 15 words is like going up Everest. Nice view, but it's cold up there. You want people to be warmed by your sentences, not falling off the end of them. Single word sentences are OK. Throw in a longer one to change the rhythm. Don't let the reader switch off - keep their attention.
Few adverbs and adjectives
Adjectives are good in small measure, like seasoning. Adverbs are the same, but are often unnecessary. It makes copy look flowery. It keeps the message hidden. So, where possible, pare down your prose to eliminate (most) adjectives and especially(!) adverbs. Use strong nouns and verbs of motion and excitement instead. And if you're not sure what adjectives and adverbs are, then it's time to find out. Now.
Learn to edit
You need to love editing. Get to love pruning, paring, rewriting. This is the process during which the diamond hidden in your lump of stone is revealed. No one writes great copy first go. Get the ideas down. Then edit.