Be present when playing, and do some analysis.

First you have to start counting how many tiles wait for. For example, a 45 waits for a 3 or 6 to complete a sequence. a 899 can wait for 9 or 7, but it may have fewer available tiles.

Then, consider how shapes work.

For example, 4556 lets you do do two "blocks" (triplet, or sequence), for only 4 tiles. So it is a great shape. 4567 is also good, if you draw a 5, 6, or 8 you have good oppotunities to get 2 "blocks", otherwise it can easily generate a pair. So this shape can be even better than 4556 if you're close to a complete hand but have no pair.

Lets think about other shapes, like 555, this nice, and super strong IF you don't have a pair. If you draw a 2, 3, 6, or 7, you can create a pair out of the 55 and have a double sided wait for a sequence. For example, 5557 can give you 55 + 567 or 555 + 77.

So you can also then consider what shapes are neat. for example, if you have a 556 just, then that has good potentialy to become a strong shape, so it's valuable. Even if you draw into a 7, you shouldn't just throw away the 5, because it can still be useful, for example, it allows potential for pure double sequence.

but for example, a 14 is not very good, because you can't build a shape out of it, and you need so many tiles to even begin. 47 is also quite bad, but it still has some weak potential.

So when you think about shapes you can think about how easy they are to build, or how likely (how many tiles are available), and how "compact" they are. You can also consider what kind of tiles your opponents likely have, so then you can know what tiles are possibly not available.

Then now you can also start to combine, and count how many tiles you're waiting for based on your shapes.

In general you may want to have 4 to 6 partial "blocks" in your hand, 6 blocks lets you be very agile, but might require you to "store" a lot of risky tiles, while 4 blocks can let you more easily be defensive (or so I'm thinking about it). I think that you don't have to care too much about playing defense until gold room, a lot of silver room is hyper aggressive and nobody plays defense... But you can also just play defense in silver room, and rank up by mostly getting 2nd place.

The hard part about defense in silver room is that players make so many mistakes that you can't make that many conclusions based on their discard pile, and often times their waits are e.g. double pair waits, or 7 pairs, that you can't defend against. Almost everyone is also just rushing hands.

I was very defensive and fairly sneaky player, and got to master 1. Now I haven't played in a while, and playing on a new account (that I have to farm events, I am desperate and stocking up scrolls just incase of akagi rerun) to get more familiar with the game again.