Sadielover's tips are all good. I also use black card between pages. The only things I would add are to scan at a reasonably high resolution, like 300dpi. If you then reduce this in an editor to, say, 150 dpi, in order to save space, you usually don't notice the difference on a monitor and it will look much better than if the original scan is at 150dpi. I like to end up with 150dpi scans because I turn magazines into pdfs and my pdf maker doesn't like higher resolutions.
Secondly, a cheaper alternative to Photoshop is Paint Shop Pro. It's a more basic program but has all the filters you really need, including the fantastic Clone tool for getting rid of tears and creases. I've tried Gimp and I think psp is a lot easier to get to grips with. Using filters is always a judgement call, sometimes they look better and sometimes they don't. If I use anything at all, at most it'll be a basic colour correction and sharpening.
Lastly, not everyone does it, but it's a nice touch to crop and rotate your scans if your scans are like mine and often not quite square
