Here are the most common mistakes people used to make when writing DVDs:

1. Not buying a decent brand (low quality blanks).
2. Writing the blanks at high speeds (highest that their optical drive could do). The depth and definition of the burned tracks was better the slower you went. It was commonly recommended to not go over 4x speed.
3. Storing the written DVDs in their original spindles. This means that the discs would rest on each other and the ones on the bottom would be pressed down by all of those above. Over 10 years this would negatively affect the tracks. Ideally the discs should be stored in disc binders, in vertical position.

By following these precautions I still have 20-year old backup DVDs that I can read without a problem. In fact most of my CD blanks have survived and are readable – and the ones that didn't owe it mostly to scratches (CDs were a lot more delicate than DVDs and nowhere near Blu Ray durability).