Before filling your potato tacos, be sure to warm the tortillas so they are soft and pliable, but not so much that they get flimsy. You especially need to watch out for this if you warm them in the microwave.  Then, when assembling the tacos de papa, be sure not to overstuff your tortilla. Fold the tortilla in half and gently press down to spread out the potato filling and seal around the edges.  Finally, when frying the tacos, only do 3-4 at a time. Keep a close eye on them and press down gently to help hold them together.