Here are some tips to help you get that manuscript as ready for readers as you possibly can -- keeping in mind that if you take out the glaring problems now, your readers will have an easier time spotting the more complex problems.
1. Go through and do a search for "was." Most of the time, when the word "was" is used, you can change it to more of an active voice. Instead of saying, "She was sitting on the porch," say "She sat on the porch." This brings your reader into closer contact with the story, and it eliminates the repetitive use of "was." However, don't forget that "was" also helps us understand when something happened. "He stood when she came in" has a different meaning than "He was standing when she came in." So don't get rid of "was" entirely - just when you can without messing up your meaning.
2. Go through and do a search for "that." Most of the time, "that" is used when it's not needed. "She thought that he'd be there to pick her up at three." Take it out and see what you've got ... "She thought he'd be there to pick her up at three." It's the same thing, but "that" gets repetitive and makes your sentences wordy. But again, the same caution goes here - don't take them all out because sometimes you do need them.
3. Go through and make sure all your punctuation is still there. I've noticed when I edit for people that as they take out words they've been told to take out, sometimes the punctuation gets taken along with it, erased accidentally by the cursor being in the wrong place.
4. Go through and take out fully 3/4 of your adverbs. Keep only the ones that are absolutely needed -- most are indicated by the context, anyway, and aren't necessary. For instance, "She whispered quietly" - a whisper is already quiet, so you don't need to say "quietly."
There you have it -- four steps to help make your manuscript ready for readers. These aren't the only things to watch out for -- there are many -- but these are the most common mistakes and the most common detractors from the story. With these things out of the way, your readers will be able to concentrate on the things that remain and help you polish the story until it shines.