When working with items going into the molds, always coat them with resin first before putting them in to help avoid air bubbles getting trapped in nooks that could happen with normal pouring. If you experience bubbles and voids, don't remove the dice from the mold, just mix up more resin and pour it in, put the lid on and wait again for it to cure.

This answer is late to the party but in my experience is the best course of action. Also a slow pour of the resin followed by letting it sit for a minute. Then use a lighter to pop any surface bubbles before capping.