As trailrunner mentions, it really depends on the tarp and what you are doing with it. Most of my tarps have either a small grommet or a loop for stakes and/or poles. So, if I'm just using the poles
along the edge of a tarp (such as to make an A-frame type tarp setup to bivy on the ground in my hammock) I put the trekking pole upside down, locked at the height I want with the handle on the ground, and the poky end in the air, with either goes through the tarp grommet or has the loop looped over the end of the trekking pole. often I may give the loop a twist or two so it's snugly on
the trekking pole tip. I then have line tied from the tarp tieout loops (the ones with the trekking
pole) to tension it. Note to get to this I usually lay out the tarp, stake four corners of it at what
I think will be appropriate width, put the poles in and erect them up and guy them off, and then adjust tension/pole/height corner stake location to get everything the way I want. Then stake/tie
off the rest. I don't think about it too much <img src="/forums/images/graemlins/smile.gif" alt="" />

If you are talking a single trekking pole for a tipi style setup, or a pole in the middle somewhere, then I have the trekking pole the other way, pointy bit down, and use the handle to prop up the tarp. This usually involves getting the corners staked/fastedn down well first then erecting the pole inside in the correct place and extending it to get everything tight. Most tarps you wanna do this with regularly will have a little reinforced place for the handle to go into.