If you control two triggers that say 'at the beginning of your upkeep' which one resolves first?

When two or more triggered abilities trigger at the same time and are controlled by the same player, that player puts them onto the stack in any order they choose (CR 603.3b). The last one placed on the stack will resolve first, since the stack is last-in, first-out.

So if you control two 'at the beginning of your upkeep' triggers, both trigger simultaneously as your upkeep begins. You then choose which one goes on the stack first and which goes on second. The one placed second will resolve first.

This matters strategically — for example, if one trigger creates a token and another trigger requires you to sacrifice a creature, you can choose to put the sacrifice trigger on the stack first (so it resolves last), giving yourself time to create the token first and then sacrifice it.

If the two triggers are controlled by different players, the active player (the player whose turn it is) puts their triggers on the stack first, then the non-active player puts theirs on top, so the non-active player's triggers resolve first (CR 603.3b).

After all triggers are placed on the stack, players receive priority and may respond before any of them resolve, following normal stack rules (CR 405.6).