Next, we'll be discussing about tenpai with no yaku having a bad shape. (And also hands that shouldn't be in damaten.)
The biggest difference between bad shapes and good shapes, is that the former will need to consider the amount of effective tiles that can turn it into a good shape. As there is very little chances of winning, if your hand value is low or the current situation is dangerous, you can choose to go into betaori.
Unless the current situation is really dangerous, there's no problem with declaring riichi with this hand.
Beginners like to wait for 4 man before declaring riichi. Everyone has to remember that the tile you want to draw right now is 2 man, not 4 man, while the chances of drawing 4 man is the same as 2 man. If you draw 5 wan first, and then draw 4 wan later, you'll be in furiten. You can see that it is not effective to wait for a ryanmen here.
There are also those who would only declare riichi if they draw 5 wan, which is also a loss. If you had declared riichi earlier, it would have the same effect as doing it after drawing 5 wan. It's very important to restrict the discards of your opponent. Not only that, while your hand is damaten, your opponent's 2 wan is able to pass and the number of tiles you can win on decreases by one.
If you tsumo 2 wan, 1300-2600 points should be a pretty good return.
Then what about this type of hand?
There are two tiles that you can draw to turn into ryanmen, but you should just declare riichi. After declaring riichi, you can win from any of the other player's discards. Even though the number of tiles that allow you to change into ryanmen has doubled, you need to draw it yourself to use it. By my standards, I will only wait for tiles to change into a better shape only if there are 4-5 types. If the current discard round is already in the middle rounds, this standard will be stricter.
Number of dora and riichi judgement
Normally, if your hand has more than 2 dora, you should just declare riichi regardless of the shape.
There are 4 types and 16 tiles that allows you to change to ryanmen when you have shanpon. Not only that, you'll also get pinfu. However when you have dora 2, there's nothing wrong with declaring riichi immediately.
If there are not many tiles that you can use to change to ryanmen when the dora is only 1, just declaring riichi is also a tesuji in modern mahjong. Getting a mangan with tsumo and 1 ura-dora is not a rare occurrence.
As for pinfu-nomi that doesn't have any dora, the return is too low, the risk of riichi is relatively larger. You can choose to remain in damaten in this situation, and going to betaori if a dangerous situation arises.
A tanki tenpai that only lacks a jantou will be waiting for tiles to turn into a good shape in most situations, the reason is that the number of tiles that you can use is a lot.
If you have 2-3 dora, you can discard 1 wan and declare riichi. If you have no dora, discard 2/4 pin and go for a tanki wait in damaten. There are many tiles that can be used to change your wait... 2356 wan, 69 sou, 5689 pin can be used to change into a good shape. Not only that, tanki wait on a guest wind is also a good choice.
Deciding whether or not to be in tenpai
In some situations where you have a tenpai with bad shape, choosing not to be in tenpai and going for a good shape is another common method. The following is an example:
Discarding 36 wan is tenpai without any yaku. However, discarding 9 pin here is a what an advanced player would do. 3456 wan is a very good shape mentioned earlier with many effective tiles. This hand will be able to turn into a tanyao pinfu. Regardless of winning rate or value, it's far superior to a 1300 points riichi hand.
It's important to be able to decide whether or not to be in tenpai. Beginners should try to understand it properly.
The next section will be about tenpai with yaku having a bad shape.