Certainly the first key is to find the "entrance wound" as described in another answer. Even then, taking small bites will still cause a jelly-lanche if you aren't careful.
The challenging jelly flow is caused by compressing both the top and the bottom of the jelly chamber while biting, resulting in a net flow of jelly out of the jelly chamber.
To avoid this, continue to hold the jelly donut with bite marks upward, but do not bite through both the top and bottom of the jelly chamber simultaneously, instead alternate tipping the donut toward and away, and biting half the filling and the top and bottom of the chamber (respectively) on subsequent bites.
Works for any high-viscosity filling. Also helpful on jucy lucy burgers, over-filled grilled cheese, densely packed burritos, and so on.