One necessary step before submitting to agents and joining in on the lovely query-ride, is making sure your work is as blemish free as it can be. More than just correcting the spelling and grammar mistakes, you'll want to be on the lookout for a few other problems that might keep your work from really shining. It's hard to be objective with your own writing, but learning how to spot the errors is an important step in mastering the editing/revision process.
Renee Collins linked to a great blog piece on something called scaffolding. I had never heard the term, but after reading it, realized it's one of those things that might slip by you because it doesn't make your writing incorrect -- only weighs it down. A must read.
Holly Lisle also has a great method for revising your work. The few steps she recommends can help cover all your bases without giving you the 'burnout' syndrome many of us experience when polishing.
And never forget the helpfulness of betas. A pair of fresh eyes will catch things you won't believe you missed.
Newbie Word of the Day: Query -- A cruel test created by agents to weed out the weaklings. Okay, not really. Just feels that way sometimes. A query is a letter or email sent to an editor or agent which details an idea for a magazine, newspaper, book or other publication, along with an attempt to sell this particular idea, along with yourself as the potential writer (a la about.com)