With tip #5 above you shouldn't have to use the despeckle filter if your image was scanned from high grade paper (e.g. Pl*yb*y, Jap mags). If your getting too much noise in your scans from quality pages lower your scan resolution (dpi). As a rule I scan at 240-300 dpi for the quality glossy pages, 120-180 for the low grade stuff. I only use the despeckle filter with images scanned from low grade paper as found in newspapers or tabloid/cheap magazines particularly when lowering the dpi isn't going to help any further because the image is already very small.
With tip #3 use a Descreen filter when scanning to help eliminate the Moire effect. Sometimes you'll find when scanning at a too higher of a resolution (dpi) you'll get a Moire effect despite using Descreen. Obviously you don't need Descreen with prints and transparencies. And if you picture is wonky after scanning just take a little time with (Photoshop) Image > Rotate Canvas > Arbitary... to straighten it up, most times I cannot be arsed to make sure the source is dead straight under the scanner lid. Oh, and save your scanned images as either TIFF or BMP. I does suck up hard drive space, but your images will be a better quality source before editing and finally saving as a JPG.
Sometimes though no matter what you do you cannot cure problems like in this stitched together centerfold image below (work in progress BTW):
The ink is stronger on one side than the other thanks to how the pages were printed. Not to mention slight moisture damage along where the spine was. It's gonna require a lot of work to blend out the colour differences.
One last tip. Buy a bottle of Isopropanol. It's perfect for spotlessly cleaning the glass bed of your scanner of greasey finger prints and any muck you cannot see but your scanner may pickup. You can even clean dirty disks with it. I also frequently use a lint free cloth between batches of scans to remove any particles that may have either floated in or been left behind by the magazine, etc. Beats editing them out later.