If you are talking about encouraging a terrestrial (opportunistic burrower) spider to burrow, I tend to try my hardest not to, because I'll never see it. Of course it's neat to see the spider do it's natural thing, but it gets old after a while... that's just me though.
For obligates and opportunistic burrowers, I would fill 2/3 of the tank up with substrate of course... you don't want too much distance from the ground to the substrate otherwise if the spider was to fall, it might get dangerous.
The best way to encourage burrowing of any terrestrial is to build a "preburrow", which includes a solid object in the tank with a small dugout underneath. The spider will finish it off for you. This'll work with most obligates and terrestrials.
I have used various objects as preburrows with varrying success. For the little guys, a thoroughly washed film cannister with the bottom 3/4" cut off works well. The best part is that you can take the bottom you cut and use it as a water dish. The top bit I just push about half-way into the substrate. They take refuge in there and then dig their own burrows.
For the large T's, I tend to use the peat pots they sell for plants. I cut them in half top-to-bottom to make two hides. By digging a bit of a scrape underneath, you can sometimes induce burrowing. That being said, some of them completely ignore the cup and just build their own burrows where they want to. Others do things like blocking off the front of the hide and tearing out the back to form a new entrance. Others will just completely destroy the cup.
The most important thing for obligate burrowers is to have enough substrate. Otherwise, you may end up with a lot of partialy-dug burrows and a stressed out T. For the G. Pulchra you shouldn't need that much substrate -- but I have never kept them personally so you may want to check with those that have before settling on a depth. If you have an aquarium anyways, it is a good idea to put substrate high enough that the T can touch the lid from the top of the substrate. In anything but the smallest aquarium, or for the pickiest T, that will also ensure adequate substrate.