Should I dig a hole in the ground before I build my fire pit over it?

what kind of fire pit are you building|?

I would cut grass out and level

Here are a few links on how to build a simple fire pit.

http://www.hgtv.com/design/outdoor-design/landscaping-and-hardscaping/how-to-make-a-backyard-fire-pit

http://www.popularmechanics.com/home/how-to-plans/how-to/g119/build-this-masonry-fire-pit/

https://www.pinterest.com/explore/build-a-fire-pit/

I have read that cinder blocks are not meant for fire pits. You might want to verify that.

It depends on how big of a fire you plan to build, you don't want too much over the top of the blocks. Since we also burn limbs that fall from our extremely huge mature trees, we are always picking them up and burning them. We have at least two and a half feet down and lined it with concrete with a smallish hole in the center for water from rain and snow to drain. We have about six or eight inches above the ground.

No you don’t need to dig. But you should consider oversizing the pit so the fire doesn’t degrade the block as fast.