when beating in at least 10 knots may be the best time to fiddle with it the first time. Your sheet will be pulled in most of the way, so for tacks you'll mainly leave the sheet pulled in and just move the traveller back and forth. On my boat in those conditions (beating in 10+) I move the traveler to leeward until the main is just getting a slight nudge of backwind from the genny right at the luff (mast side of mainsail) for max speed. your boat will be different, nothing more fun than watching the speed meter (gps, whatever) in a steady wind and tweaking tweaking tweaking to find the sweet spot. Anyway, those conditions will probably reveal the traveller's part best IMHO. Get everything trimmed tight, then move the traveller back and forth and notice the effect on speed and heeling. Interesting stuff.
Basically my sail trim routine looks like this after every tack/jibe:
1) genny shape - this mostly involves getting the right spot on the genny car track and sheeting. The cars move based on wind conditions, I pretty much know my boat and can just set them now but sometimes they need tweaking. set the leeward car, see how that works after a tack/jibe, then repeat.
2) Main sail shape - main sheet and
boom vang control this.
3) Traveler location - conditions dictate.
4) readjust starting at #1 -> #3 until satisfied.
(masthead
rig, tall thin main)