For most people, the best indication of MINIMUM amount of increase
is the difference between their PreTest scores and their own SATVerbals,
converted into LSATs as a one-to-one translation (SATVerbal of 610
= LSAT score of 161+).
Of course, many people outperform their own SATVerbals. The amount
of increase is usually more limited by time than anything else.
If everyone trained for a full year, as some PreLaw Advisors recommend,
increases would be much higher than they already are. For most people,
you can assume a probable rate of increase of anywhere from 7 to
10 points per semester of training. So if you want 20 points of
increase, you should be ready to train for anywhere from two to
three semesters, on average.