A huge part of maximizing the effect of inside english, is figuring out how much you can cheat the pocket. It makes a very big difference in the final position of the cue ball. And it's challenging when you have deflection changing the angle.
I think the way it works is... for cuts under 45 degrees, you're looking to hit the object ball
as fat as possible without missing the shot. This sends the cue ball more 'forward' towards the first rail. The idea is that the line the cue ball takes to the rail, is as close as possible to the the direction you're trying to send it.
In this first example, I'm trying to spin the cue ball as much as possible to my right. By hitting the object ball as fat as possible, I send the cueball along the orange line to the right.
If I hit it as thin as possible, the cue ball travels on the black line. Then the spin doesn't seem to help as much. The same amount of spin takes me only to point "B" instead of point "A".
-----------------
For cuts over 45 degrees, you now want to cut as thin as you can get away with, but the final goal is the same... to send the cue ball on a straighter path to the first rail. In this example, a thin hit lets the cue ball contact the rail a bit further to the right than it would with a fat hit (the red line). Since my goal is to have the cue ball end up as far to the right as possible for position on the 9, I consciously overcut this ball a smidge, hoping to hit the first rail as far to my right as possible.
Three other tips:
• English takes best at slower speed. If hitting it softer means you also leave a longer shot... you may have to make that sacrifice in order to get your inside spin to 'take'.
Harder hits also cause the cue ball to deflect more to the side after contacting the object ball. Since the goal is to make the cue ball run to that first rail as straight as possible, hitting hard always works against you by sending it more 'sideways'. Unfortunately there's sometimes no choice.
• To maximize inside english, you want MIDDLE sidespin action. You might be required to add some top (or draw) but you want to use as little as you can get away with, because top or draw will 'dilute' the sidespin. You can't hit as far off to the side once you add high or low to your shot.
Notice in my first diagram, the contact point is only a little high, and lots of right.
There will be some cases where you hit with middle right, but after travelling a while, the cue ball picks up some forward roll from the cloth. For example in the second shot, if my cue ball is a diamond further away, my middle right might act like high-right by the time it hits the rail. The topspin it picked up is diluting the sidespin. So to compensate, I hit just a bit low, and soft like a draw-drag shot. By the time it arrives to the rail the draw has worn off, and what's left is (almost) pure sidespin.
• Don't be afraid to hit a little further off to the side than you're comfortable with.
==============
As for help with the actual aim and deflection... this will start an ENDLESS argument, and I apologize in advance, but all of this stuff is easier to aim with a low deflection shaft, unless you've spent like 20 years with a conventional shaft. You don't HAVE to use an LD shaft, you can do the same shots with the same spin using ANY shaft. The LD shaft just changes where you need to aim to make the shot. And to me, that aiming line is lot more 'common sense' and natural with an LD shaft, whereas a conventional shaft's aiming line looks weird. Your mileage may vary.
Beyond that there's no magic bullet except to set up a few shots (like the ones in the diagram) and practice them a ton. Focus on middle sidespin, way off to the right, and aim to hit the full side or the thin side of the pocket. Hit softly so the english takes, using only the barest amount of top or bottom needed.