Editing one's work is important, and never more so than in the self publishing game, since the writer is often the only editor that is going to look at the work before it is presented to the public at large. That's a pretty scary thought when you think about it, which makes it all the more important to do the job properly in order to ensure that the writing is of the highest quality possible before others get to see it and judge you on it. Fortunately, there are some relatively easy to follow tips to revise your work.
Reading your work aloud can be a good idea. Just re-reading the text isn't enough - sometimes you can be too close to it to see something that isn't particularly well written, or doesn't really make sense, but when you read it out loud it can be much easier to spot passages that simply don't work or read very well at all.
One basic rule of editing that will probably always apply is - when editing, you lose text, don't gain it. This means that you don't start adding material in. The purpose of the editing process is to lose content that's overwritten, too wordy or doesn't make logical sense, not to start rewriting from scratch (not unless you suddenly realise that the whole thing is rubbish, anyway).
p.s. There's no room for sentiment in editing - you must ensure that the harshest critic of your work is you.