Mahjong is a complex game, and the Japanese variation is no exception.
Waits
A wait are tiles you do not possess in your hand, but you seek them either by draw or discard. Knowing the waits is essential to hand development. The process of identifying waits occurs throughout the game of mahjong: from the starting hand, interim, and to the state of tenpai. In particular, it is important to note these waits during tenpai, or even beforehand, to avoid furiten.
In addition, the type of wait used during tenpai for the winning tile(s) may factor into the amount of minipoints, or fu. Fu is relevant for any hand scoring 4 or less han.
Open wait
| 1 | 4 | 7 |
| 2 | 5 | 8 |
| 3 | 6 | 9 |
Open waits, or ryanmen, are two or more types of tiles being waited on. These apply to sequences, or shuntsu.
For example:
.
This pair is waiting on either a 
or 
to complete a meld.
For these waits, they follow the pattern on the "mahjong octaves" table.
Closed wait
A closed wait applies to shuntsu in which the middle number is the tile waited on.
For example:
This example pair needs a 
inbetween the 5 and 7 for completion.
Dual pair
The dual pair, or shanpon, involves a wait to complete one of two pairs of tiles. This generally applies to hands in tenpai. So, in addition, the other 3 melds are already complete.
For example:
To complete this hand, only one more of either the 
or 
are needed.
Pair wait
Pair waits, or tanki, are waits for a single tile to complete the pair. Typically, this applies to a hand in tenpai which the hand is already composed of four melds and the pair is left incomplete.
For example:
The example hand already has the 4 main melds completed, and there is a single 
waiting for another 8 to complete the pair.
Other wait patterns
The above are the basic wait patterns. More complex wait patterns may occur, and often, they involve a combination of the above waits, particularly involving the open wait (ryanmen). These involve waits on 3 or more tiles and may be explored separately.
Offensive play
Essentially, the game of Japanese mahjong is a 4-way race towards tenpai and ultimately winning the hand to accumulate points.
Open vs Closed hands
Aside from tenpai vs not in tenpai, a mahjong hand may be characterized in these two states: Open and Closed. It is important to know when to determine the time to open the hand and when to remain closed. This decision may be affected by the hand's composition, which looks for any yaku.
Therefore, familiarity with the list of yaku greatly aids with this thought process. Other factors may include: the state of the other players, how many tiles are remaining in the live wall, and/or the need to go on the offensive or remain defensive. Combined with a particular yaku, opening the hand increases the speed of development leading to tenpai. If this is the player's current goal, then opening may be advantageous.
Typically, an opened hand results in a decrease in value. Many of the yaku listed decrease by a yaku of 1. For some yaku, the state of open vs closed is irrelevant.
Defensive play
While Japanese mahjong is often a race to be the first to tenpai and win, it is also important not to lose points. Especially when an opponent has declared riichi, the game becomes a form of "minesweeper", where the objective changes to not playing into an opponent's hand.
In this case, it is important to note the discard pile.
WWYD
WWYD, or What Would You Discard, is a puzzle, in which a player may examine the state of a hand after a drawn tile with or without a given scenario. As in the case of mahjong, a player must decide what to discard during his/her turn. WWYD is a screenshot of a mahjong hand during this state. As players, it becomes the objective to make the best decision regarding the impending discard. WWYD helps players make thorough considerations on a discard, without the time pressure of an actual game.