How to roll a seed you can verify: what actually costs you entropy, what is not worth worrying about, and what each wallet does with the rolls once you hand them over.

The short version:

Use the dice you have, roll the count your wallet asks for, and you are done.

• Cheap board-game dice will do. Casino dice are provably fairer, but would have essentially no impact on your seed (§2).
• The math says more rolls are not necessary. Your wallet’s count already fills the seed (§3).
• Give every roll plenty of tumble. The one part worth your attention. Shaking dice in a box takes care of it (§4).
• Do sets of test rolls and cross-verify with multiple tools. Roll them for real, then discard them (§5).
• There is no one standard. This page documents five methods across 17 implementations. Look up your wallet (§7).