Have a look at Rip's article Incremental Increases
Essentially, you go to smaller jumps when the larger jumps are not sustainable. Note that the smaller the jump, the more you need to pay attention to the accuracy of the equipment - don't assume that the listed weights are correct (here is one recent example). The simplest way to keep things in line is to use the same equipment every time.
At some point, program reorganization yields more progress than adding a small amount of weight every session.