I too have trouble with serve return and there is some great advice here BUT... if we are supposed to move before ball hits the servers racket, how the -beeep- are we supposed to know whether the serve will be to FH or BH?
Here: part of the idea is that, if you are not moving, it is much harder to start moving. Think of standing flat footed and then trying to run from there. For the first few steps it will be hard to accelerate and then as you are moving it becomes easier to accelerate. For this reason, when you see people running for exercise in city streets, if they come to a crossroads where there is traffic and they have to wait, a seasoned runner will jog in place until they can accelerate forward again. From jogging in place, they will be able to accelerate forward much sooner than the runner who just stands and waits.
If you watch what the pros do when receiving serve, as the opponent tosses the ball, they go from low to high, and as they do they move a tiny step closer to the table so their feet are already moving before they commit to where they think/see the ball is going. But, you can also see from body position, body language, and racket angle, before the ball is contacted where the ball may go. You just don't want to commit till you see where it actually is going. But you still can take a very small step in the direction you sense the ball will go. That won't prevent you from changing directions.
The idea of being just far enough back that you would even want to move in a hair on a long, fast serve ensures that, if all you do is move in a tiny step towards the table on the serve, that you are going in the right direction no matter where the ball is actually served.
One more detail. A TT table is 5 feet side to side (approximately 152.4cm). A human adult's arm is, on average, somewhere between 20-30 inches (51-76mm)[more than 1/3 of the width of the table]. If you are standing solidly in the BH corner, the most you really would have to move, given the arm length, from the BH corner, to cover the FH corner (if you cut off the angle and take the ball off the bounce) is 1.25 feet (38cm). We are really talking about very small adjustments to positioning on return of serve to make it so your feet are in place to take a good stroke.
A good part of what a player not skilled at those small, simple movements do is:
1) Start late.
2) Rush because they already are starting from behind the 8 ball.
3) Make too large a movement because they think they need to move farther than is the case.
4) or, not move at all and just reach and therefore force themself to take a shot with suboptimal mechanics because their arm is contorting or reaching to make the shot.
For MOG, there are many many many times when the serve is to his switching point and, in looking, from my vantage point, it seems the obvious shot would be to turn to his FH to return the serve. However, instead, he does not move his feet, he does not move his body and he moves his arm over to take a funny BH with the arm way too far towards the FH side.
One thing I would actually think about trying for a few weeks if I was MOG is, try to make it so, every serve that is anywhere closer to the FH side than 1 foot from the BH side line, he should try to turn and take that with a FH. I will restate that again. This would be an exercise. He would have to forget about winning points for about a week and commit to trying this. The only serves he would receive with his BH would be closer to the BH side line than ONE FOOT (30cm). Everything else, he would have to try and turn to use his FH. That would be the footwork of the turn in a Falkenberg from the BH to the first FH. That footwork, legitimately, can make it so you can take any serve between the two end lines with only your FH. I have seen decently high level players return serves that were several feet wide of the BH side line with their FH. But this would only be so that, if there was any serve where MOG had to move at all towards the FH side to take a BH, that, instead, he would turn to the FH for ALL OF THOSE SERVES.
After about a week of trying, he should start having success doing it. That is my guess. That movement is also a pretty small movement relative to how one might think of it. It is one normal sized one step while turning open for the FH.
But this would not replace getting his feet moving while the server TOSSES the ball.
BTW MOG: as I see it, you are playing pretty well. So keep up the good hard work you have already been doing.