10 Very Basic Rules when Scanning Film Negatives and Slides

1. Have fun! Treat scanning as an enjoyable hobby. This is not your job! Listen to some of your favourite music while you are at it :)
2. Be patient and take your time.
3. Learn to use the scanner software, even if it seems difficult in the beginning.
4. Wash your hands with warm water and soap before handling films.
5. Touch the sides of film negatives only. Handle your films with care.
6. Use a Bulb Blower to remove dust from films. You will typically get this with your SLR camera, and it is very cheap. Do not blow on the film to remove dust, as small wet drops will be visible on the final result!
7. Be very very careful if you are about to clean a negative film or a slide. It is possible, but if you do not have the right equipment, chances are high that you WILL DAMAGE the film/slide! More often than not you are better off doing some post processing of the scanned image. Very dirty films can be cleaned, but you really must know what you are doing. Do not attempt to clean the films with a cloth or paper, you will only end up making bad scratch marks. A very soft specialized cloth can be used as long as it is new, but it's quality will quickly degrade.
8. Never - ever use your fingers in an attempt to clean the films! This is true even if you have very carefully washed your hands. It is very tempting to give this a try if you spot a small hair or similar, but I am telling you; You Will Regret it. 
9. Use a white surface or a lightboard when sorting negatives. A good working lamp helps a lot.
10. Do not scan every photo you have. You don't really want to keep that blurry photo of your neighbour's car.