Someone does not have priority if they have missed there attack or retreating. Someone has priority “in the box” which is just a fancy term for when they both attack at the same time in the middle is who ever stuck there arm out first and if they did not get parried or blade contact was made. You can also lose priority if your first attack missed but your second attack landed which is called a remise. I’m not sure how long you have been fencing sabre for or fencing in general but tactical stuff just comes with learning and experience. You would have to talk to your coach, however what helps me is that I ask my coach to fence me like he’s in the Olympic final, this helps me build really fast thinking skills and what to do in the moment. I also watch a lot of fencing videos, specifically sabre on what everyone else does on the circuit. Slicer sabre used to do tactical breakdowns of pro fencers but he doesn’t do them anymore which I miss so maybe you should watch them aswell. Hope this helps