Is there a secret to toasting chiles?

I think it’s so important to toast dried Chiles the right amount of time, because over-toasting leads to bitterness that can ruin a dish, and under-toasting can result in a more bland dish.

Because of that, I always err on the side of under-toasting and feel like I can get more flavor, but it seems like such a thin line between the best flavor and when it starts to become bitter.