I cut off a sucker on one of my fig trees, it's about 1.5 feet long and there are some roots growing on it already.  What's the best way to propagate the sucker?  I currently have it planted in a 1 gal pot with potting soil, should I cut off all the leaves?  What should I do to give it the best chance to survive?

No expert here, but I'd keep it in the shade for a while and make sure it doesn't dry out.  I'd maybe get rid of the lower leaves, but I wouldn't cut them all off.  If you want a tree form, I'd let it be.  If you like multi trunks, I'd cut off the top 3/4 inches to encourage branching.  Yup, that's what I'd do.  Good luck with it!

Cheryl is right on. My Osborne's Prolific suckers profusely.
Soak the pot in a liquid rooting hormone for a day.
Snip the tip to get it to branch out.

I did this two years ago when I pulled a sucker of my Violette de Sollies with roots while the tree was green. I killed it.
Two weeks ago, I snapped a sucker from a golden Celeste, divided it into four cuttings and stuck them in soil. Two already have new leaves and hopefully growing.
I call this a 50-50 % chance.

Leave it long, moist soil not drenched, moist air not hot and dry, if the leaves wither it means it doesn't have enuf roots to sustain it and there is a chance it may die, cut it in half, and try to root the top like you would a cutting. This would give you the best chance of survival.