Well, first, how long has it been sitting quietly in a drawer? If this is your first novel, the story could be so clear in your mind that you're going to miss things that you believe
should be there, but don't actually appear on the page.
The best way I've learned to start the editing process is to get the required distance from my memory of it that I can see the problems. I'll write on something else for a few weeks and then come back.
Now, if you've already done that, then what works for me is to read it all the way through like you would if you were a reader just buying it. Don't actually make edits on the first pass--even though you'll want to. Just make a red star or X on pages where you see problems. You might even make a code, like * for typos/misspellings, X for plot problems or # for dialogue that sounds wooden or stilted. You can make as long a list of codes as you like, or none at all...just so long as it makes sense to YOU. Once you've finished the first reading pass, take the time to really think about the plot. Was it believable? Did the characters seem like they belonged there? Did the characters eat, drink, sleep? Was there enough time given in the plot for real world things to occur (repairmen not showing up on time, paying bills, shopping, weather, etc.)?
Fixing those things might mean characters need to move or be eliminated from a scene, or new characters added. Then, once you've got the characters where they need to be, you can concentrate on dialogue, word choice and other small things. Like most things in life, start with the big stuff and don't sweat the small stuff until the small stuff IS the big stuff.
