I train in a 4-6 repetition range using the Max-OT principles. I select a weight that allows me to get at least 4 reps on my own but no more than 6. When I get to the point where I can complete 6 fairly easy reps, I increase weight.
After each workout I record the weights I use so I can refer back to those numbers the following week. This way I know the exact weights and reps I need to work to exceed.
Make it a goal to improve each workout by either increasing weight or completing extra reps. Working to better your numbers each week will keep pushing you to perform at a higher level in the gym.
Remember, you don't have to make huge jumps in weight to be effective. Small increases add up over time and progressively overloading your muscles with the Max-OT principles is the key for continual strength and muscular development.