Here are a few basic tips I follow when editing. Feel free to add in your own.
1.) Does your character do something too much? Giggle? Blush? Belch? Brush her hair aside? A character only has to do these things a few times for the reader to understand it's part of the character's personality. Brutally cut the rest.
2.) Don't be redundant with dialogue tags. It is not necessary to write, "But why can't I go?" she asked. It is not necessary to write, "She's always gets her way!" he shouted. And a conversation between two people needs very few dialogue tags at all. Don't burden your dialogue (and word count) with he said/she said. Make your tags count.
4.) Be refreshing. Use the search mechanism on your document and find words you use too much. Then visit your friendly neighborhood thesaurus to get rid of boring/over-used words.
5.) Be methodical. Read your manuscript over for typos only. Then read it over for numbers 1-4 only. Then read it over for voice/craft only. Isolating one problem at a time will help you make sure you didn't miss anything.
6.) Above all else: First draft work is zoo dirt. Don't send an agent/editor zoo dirt.