Well, you've started the process already...now it'll just need a few years to grow.

If you want to keep the plant real small, you can start pinching back tip/top growth as soon as it has a bit of trunk to hold upright.

If you want a bonsai with a thick trunk, you'll need to allow the plant room to grow - which means a container slightly larger than would usually be suggested for a jade; or you could plant the jade in the ground (if your weather allows for it). Pruning will also encourage a thick trunk. In five years, you will have a decent specimen.

Now, realistically, it's easier (in my opinion) to start a jade bonsai from a cutting that already has some of the upper foliage features (branches/leaves) that you desire. If you start with a thickish trunk, it'll thicken that much more when you prune it.

Another tip has to do with the root-flare or nebari.
At some point, you'll want to have a look at the upper roots to see if they're wrapping around each other. If you can get them to grow outward, in a radial fashion (like spokes in a bike wheel), you can later select the largest and best looking for presentation. Smaller or uglier roots can be trimmed away.

Josh

This spring, I bought a jade from Home Depot for $10.00. The base of the plant had a nearly-2" diameter trunk, but was badly grown and very top-heavy. Just above the base, the plant forked into 2 secondary trunks. I cut off one of these trunks and rooted it. I then drastically pruned the mother plant, and rooted all the stems. Then I barerooted and arranged the roots in a nice pattern, and repotted. As the plants became established, I defoliated almost completely, leaving only small leaf buds. New leaves are popping out all over the place. I am rooting the leaves that I removed.

I now have one plant that already has a decent trunk, a half dozen or so plants with smaller trunks, and dozens of rooting leaves; all for $10.00.

Cheers!