As far as I'm informed:

- Burn ISO slowly (4x)
- Use good DVDs (DVD-R and do RWs)
- Don't use cheap burner

- For DL discs sat the layerbreak to 2084960 (Super Smash Bros. Brawl is the only game using DL so far)
- For DL discs DVD+R DL should be used, preferably Verbatim