My croton is quite leggy and I'd love for it to become bushier. How can I promote growth from the bottom of the plant?

The only sure way to get lower stem growth is by cutting any stem all the way back to the point where you would like to see that new growth. That is because almost invariably, new growth comes in only at the tip ends of each stem, not lower down.

Another option is to constantly pinch out new growth as soon as it first emerges at the end of any stem. That will keep that stem from growing longer and very occasionally may cause new growth to emerge lower down on that stem.

Lovely Crotons (Codiaeum) and I agree with Will on pruning. We have a few on the side of our house that got hit hard by cold this winter. I pruned them all back a couple of weeks ago and noticed new growth when I was outside today.