It’s very easy to get yourself in a situation where you’re unsure which aircraft you’re following after being sequenced by tower. Here’s an example with a technique I use to simplify fitting myself in.
Say you tune into tower at a multiple runway airport with parallel runways. Tower tells you to enter L downwind runway L, #4 traffic to follow is on L downwind. Sounds simple enough, but what if there are 4 planes on L downwind, 3 on R downwind, 1 on final for L and 2 on final for R. Since you didn’t hear how tower sequenced the other aircraft in the pattern, There’s absolutely no way to determine at this time exactly who you are following!
Here’s the trick. Watch your spacing and enter downwind. There’s one on final for L, so he’s obviously #1, just stay on downwind until you see two more aircraft turn final for L. You now know it’s safe to turn base and final, as you’ll be the 4’th aircraft on final after being sequenced.
This works every time!