I use the same soil principles for figs as my other trees. The only caveat is that figs care less than most other fruit trees about soil conditions. I get the feeling that they don't mind subpar soil (not promoting neglect!) and are rather like weeds.
The most important thing in my opinion is the draining. BTW if you get a good amount of rain, it's a great idea to plant it in full sun + on top of a slope/incline to have all the water wash down away from it if you have that option. The draining as far as I'm concerned is important for fruit flavor. You don't want figs ripening while water logged. That is for sure.
People tend to be overly critical of their yard's soil almost to the same extent people tend to overestimate the amount of sunlight their yard receives :). Not all clay is equal and most is actually good enough--and packed with nutrients. The number 1 mistake you can do is to dig out a hole of all clay and put in 100% well draining soil. This is referred to as the clay jar effect, where the clay surrounding the tree a couple feet away locks in all the water into that nicely draining soil. Basically you've now created a sponge where all the water goes and stays! Also the roots will eventually hit your native soil--especially figs they seem to send roots everywhere and far out for me. So if you spoil them will all this nice soil to stay in for the first year or two then they may get shocked a bit when they eventually have to acclimate to the somewhat crappier native soil.
Here is my bottom line way I generally do it although you may have really bad soil it's possible this is a bad idea if that's the case but I doubt it--if you have the typical clayish soil in yards around my parts (red is generally good, white clay is generally not so good) then:
I dig a hole, mix in 50% regular old top soil with 50% native soil back in. That's it.
Lately I haven't even been amending with 50% top soil. But that seems to be a winning, simple, and cheap formula for 90% of my fruit trees. Instead of 50% top soil, I'll use 50% peat moss for blueberries. And if it's something like a fig or pomegranate I believe aren't as finicky about soil conditions--I'll sometimes just forget any amendment all together.
To amend the soil in the long term, apply a couple inches each of compost and mulch every season and within a few seasons--gradually--the soil will become better.