Watch the Luff
Same as for a regular spinnaker: Ease the spinnaker until it just barely begins to luff, and then sheet it in a touch. Properly, it's a full time job for someone without neck problems to constantly watch the luff... easing the sheet enough to get a slight curl on the luff and then tightening again. As you go from a run to a broad reach to a beam reach, the sail will be sheeted in more and more, of course. You'll know you're trying to go too close to the wind when you can't sheet it in any tighter yet the sail's still luffing. That's because there's no forestay to control the shape of the luff and of the sail. And that's why your jib/genoa IS attached to a forestay. And that's also why you can generally point higher when: the forestay very tight (and straight); the halyard and/or cunningham is tight (moving the draft aft); you have a new, stiff, non-stretched, non-baggy sail. (If your spin's undersized -- if the luff is short enough (less than forestay length), you can crank hard on the halyard or tackline tension to point a little higher... but don't rip your sail!) Baggy is good downwind, not good upwind.
