How low should I let the battery of my iPod go before charging it, especially the first couple of times?

I have a new battery in my iPod touch. The manual says to let it discharge the first few times all the way, so as to properly condition the battery.

But what does "all the way" mean in this context? Do I start a recharge when the 20% warning shows up? Or use it til there is really no charge left at all? Or something in between?

Thank you for your help.

Polly