If you are the type of player who has trouble generating power when looping, try out these two tips, and you'll be surprised at the improvement.

First, keep your legs farther apart, i.e. a wider stance. This makes it easier to transfer weight into the shot, meaning more power. Watch videos of the top players and you'll see how they all keep a pretty wide stance.

Second, contact the ball more from your side. Many players contact the ball too much in front of their bodies, and so they get power mostly from their arms. By contacting more to the side, you get more natural body rotation into the shot, meaning more power.

Third, tilt your wrist slightly back. This will naturally give you more wrist in the shot – and you'll likely use more forearm as well as you use it naturally to snap the wrist into the shot.

By following these three tips, you'll get more power without really trying since none of these involve trying to "muscle" the ball – it's all about good habits that allow you to maximize your natural power. 

Many players develop pretty good strokes, timing, and footwork, and in practice drills, where they know where the ball is going (i.e. rote drills), can execute them pretty well. But once they get into a more random drill or game, where they don't know where the ball is going (i.e. forehand or backhand), they fall apart. How can you fix this problem?

The key thing here is reaction. Once you have good strokes, you can do various random drills such as having your partner or coach randomly block to all parts of the table while you loop or drive them back to the same spot, or serve backspin that your partner or coach pushes back anywhere and you have to loop. (Focus on a good neutral position, react rather than trying to anticipate, and step to the ball.) These are excellent drills. But many players struggle with them, and don't get enough practice time on these types of drills to progress as fast as they'd like.

There's a simple alternative. Find someone who can help you out – it doesn't have to be a table tennis player, it can be a friend, spouse, son/daughter, anyone – and simply have them randomly point left or right. You react by shadow-stroking either a forehand or backhand, depending on which way they point. Or, if you want to get fancy (and more closely mimic a game situation), have them toss balls at you randomly, forehand or backhand, and you react, either by shadow-stroking, or actually hitting them with your racket. (It's basically multiball, except since they are tossing the ball at you instead of hitting off a racket, anyone can do it.) In both cases, it's not exactly the same since you aren't reacting to a ball coming off a paddle, but it's reasonably close. 

Then watch as your apparent reaction time in game-type play improves! It's all about zeroing in on a weakness, and practicing the specific thing that you are having trouble with. The principle applies here and in all other aspects of table tennis . . . and life.

And a call for help – can anyone design a simple phone app or other inexpensive device that randomly points left or right so a player can do this solo?
EDIT: And from the comment below, here's the solution - Table Tennis Edge!

It's easy practicing topspin rallies since you can do them over and over in the same rally. The same is not true for practicing against backspin, unless you happen to have a chopper to practice with – and that's not quite the same either, since a chop against topspin comes out differently than a push, and you don't get practice switching from playing against backspin to playing against topspin or block. So how should you get your practice against backspin? There's a three-step process.

1. Multiball. Here's where you learn and hone the forehand and backhand loops. You can do this with a coach or a practice partner where you take turns.

2. Serve and Loop Drills. You serve backspin (usually short), and partner pushes it back long so you can practice looping. In each case you should play out the point. There are four main variations of this given below, in progressing difficulty. In all four of these variations you should probably do your first loop to the same spot each time so you can start off each drill with your partner making a good block. You might also arrange so your partner's first block goes to the same spot, depending on your level. For example, your first loop might go to your partner's backhand, he blocks to your forehand, and then you play out the point. There are many variations of these drills; decide what you need to work on and design the drill around that.

• Partner pushes to one spot, such as wide forehand or wide backhand, and you forehand or backhand loop, then play out the point.
• Partner pushes to wide forehand or middle and you forehand loop, or partner pushes to wide backhand or middle backhand and you backhand loop. While you know in advance whether you'll be doing a forehand or backhand loop, you now have to move to do so. Note that you should generally cover more of the table with the forehand (where the body is not in the way so you have more range, plus it's usually more powerful), which is why the backhand drill covers less of the table. But if you prefer backhand looping from the middle, make that adjustment. If you are a forehand player who covers a lot of ground with the forehand, then have them push to 2/3 of the table, or even the whole table, and you follow with a forehand.
• Partner pushes to either wide forehand or wide backhand and you have to react with either a forehand or backhand loop. Partner should practice deceptive pushing starting here – sometimes aiming one way, then going the other direction, and try pushing quick off the bounce.
• Partner pushes anywhere randomly and you have to react with either a forehand or backhand loop. Again, partner should sometimes aim one way and then go the other way, quick off the bounce.

3. Improvised Games. Do the very same drills you did in the Serve and Loop Drills, except now you should play games that start out in these ways. Keeping score makes sure both players fight hard, and very closely resemble real game situations. Choose what's needed for you. At the advance levels mostly use the variation where your partner pushes the serve back anywhere and you loop, and then play out the point. 

A common problem when facing a weaker player is literally go into the match with the tactical plan of not playing your best. Rather than play your normal attacking shots, you play soft, hoping not to risk the more difficult shots that make you the better player. It's often a mistake. 

This doesn't mean you should be ripping shots left and right against a player where you could win without taking such risks. But if you are used to mostly attacking at a certain range of speeds off a given shot, and hold back on this to play "safe," you're more likely to both miss the shot while giving the opponent an easier shot to respond to. Holding back usually means you take conscious control of a shot to soften the shot for "safety," which means you are throwing away much of the muscle memory you've trained so hard to develop. Result? You play soft and erratic, and the opponent has shots to tee off against while not facing your best shots, the very ones that made you the better player. That is risky play. 

So it's usually best to just play your game against a weaker player, focusing on the type of tactics that will allow you to play your best game without playing overly safe or risky. By doing so from the start, you spread the "risk" over the entire match, and guess what? While individually some of these aggressive shots might be "risky," the risk goes away if spread out over an entire match. If you would normally loop a given ball rather hard, then do so, and let the muscle memory guide you. 

At the lower levels, pushing is often over-used, but at the higher levels, many underestimate their value. All top players have excellent pushes. However, advanced players - and even intermediate players - rarely push against deep backspin to the forehand, unless they are choppers. (And even choppers will often attack them.) It's simply better for them to attack, usually with a loop. (The same can be said on the backhand, if you have a good backhand loop.) So … should you develop your forehand push?

The answer is yes - but not necessarily against long backspin to the forehand. You need to develop your forehand push mostly against short backspin to the forehand. Against this ball, you can attack, but pushing is often the better bet. You can push short, push quick and long, go for angles, heavy spin, etc. - all sorts of variations. And because you are closer to your opponent, he has less time to react. (At the same time, don't predictably push - learn to flip short balls as well.)

The problem is how do you practice your forehand push? If you push forehand to forehand with a partner, then unless both of you are practicing short pushes, you'll be practicing pushing against long balls. The answer is to develop the forehand push this way with a partner, but once it becomes relatively advanced, start focusing on drills where you start the drill by pushing against a short backspin, and then continue the drill/rally with other shots. You won't get as much repetitive practice this way, but you'll practice what you need to develop. For example, your partner serves short to your forehand; you push quick off the bounce to your partner's backhand; he pushes quick to your backhand; and you loop, either forehand or backhand. (Or, alternately, your partner loops off your forehand push, if it's "his" drill - and you still get practice pushing!)

Meanwhile, a nice drill is to push forehand to forehand (or backhand to backhand) where both players push short - but the first time a player pushes long (by mistake), you loop. This develops your short push, develops your loop, and best of all, it develops your judgment on whether a ball is long or short.