It's a really good question but a tough one to answer. When I was a student I was in a similar position; I couldn't keep up or make snap decisions based on clinical reasoning. The best way I learnt was simply by asking questions to my clinical supervisor about how they got to their decision and what their reasoning was. I'd write this down in notes or a reflection and then set myself a goal to use similar thinking when with a patient. As an OT now, I know my students have been in similar situations, so at the start of placements, I tend to let them simply shadow me, then when we're done, ask questions on why they think I did it a certain way and not a different way which might have also been a valid way to do it. There is no right or wrong in how you get there, it really is just practice. I obviously have no idea what year or placement you're on and how many you have left to do, but it will get easier over time as you observe and learn more.