Daisy,
If it's any help to you, there's a brilliant book about writing, called 'On Writing', by Stephen King. You can get it in paperback and they sell truck loads of them. Regardless of whether you like horror or Stephen King, it is an excellent little book about the writing craft. It contains some wonderful tips for writers and I have named it my writing bible, it's simply that good. King never revises something until he's left in a draw, six weeks after he's finsished it. He suggests that six weeks is a long enough piece of time to be able to look at what you've written with fresh eyes etc.
I hope this bit of info. helps you, the book most certainly will. I think, and I'm no one to even begin to comment, that revising something is to take your writing to it's extreme possibilities in the story you are telling. To be able to fix any plot holes, mistakes, errors, whatever and make the writing a solid piece of writing. If people suggest taking things out, or adding, think carefully because remember, you're the writer and you are the one that has to feel satisfied and happy with the finsished piece. The reader is just a reader and King suggests that the aim of all good writing is to make the reader unaware that they aren't reading.
Hope some of this helps, just do what you feel right in what you write and you cant fail.
Welcome to WW, it's a great place to get feedback.
Steven McNay