How much weight you should add?

Does anyone have any reccommendations on how much weight you should add to a routine after fully recovering a muscle group (f.ex. percentage of 1RM)? I sometimes find it difficult to find the ideal weight on a single set to fully fatigue the muscles in the lower rep range (1x7-9).

Do you mean, add relative to the previous
workout?

It comes down to past experience and
training logs, referring back to previous
training cycles, and possibly with the
aid of having noticed things such as that
for you on this particular exercise
increasing weight by 4% 1RM decreases reps
by one, or whatever the case may happen
to be for you.

Also, regardless of whether the weight you
choose winds up allowing you only 4 reps
or allows you 10 reps (or even more) you
can do as many reps as possible with that
weight, and get good training effect, so
I’m not quite sure what you mean by finding
it difficult to find the ideal weight to “fully
fatigue” the muscle.