Honitsu
Honitsu is popular with beginners because it feels easy to build.
You can often make it in a mechanical way just by collecting one suit plus honors.
In reality, Honitsu really is fairly easy to make, and it is valuable, so it is one of the yaku most worth aiming for.
The places where players truly separate themselves with Honitsu are how they call and how well they understand the remaining shape.
You often see people fail to call the tiles they should call,
or call tiles they should not call and end up missing the win.
Hands You Should Not Open
Even when opened, Honitsu is still worth two han,
so there is usually no need to cling too hard to staying menzen.
So then, in what kinds of cases is it actually better not to call?
Example 1
With a hand like Example 1, you can clearly make tenpai just fine while staying closed.
If calling would turn it into a cheap open Honitsu,
and the hand also still has Ittsuu attached to it,
then you should hold off on calling as long as possible and aim for a closed Honitsu.
By the way, in Example 1, drawing any manzu tile gives you a tenpai shape that is at least a ryanmen.
This is a somewhat extreme example,
but if you already have a good one-shanten shape for a closed Honitsu,
then it is worth trying to finish it menzen.
Example 2
With a shape like this, it is very common for something like or to already have two copies discarded, turning it into a dead pair.
Many players act as if that does not matter and just keep ponning everything anyway.
But when you have a dead pair, the better route is often closed Honitsu Chiitoitsu.
Example 3
The most common failure is starting to call from a hand like Example 3,
before the meld structure is really in place at all.
Pon 
In a case like this, you should first stay closed a bit longer and tidy up the hand shape.
The remaining shape is simply too miserable.
If someone riichi's after this, you have no strength to push back,
and the price of losing a safe tile like is too high.
Which Tiles to Call, and Which Tiles to Pass
The most important point when calling for Honitsu is:
do not split your hand apart.
Example 4
Pon 
There is one tile in Example 4 that you absolutely must not call.
It is .
Pon 
Pon
Once you pon it, and become extremely hard to use.
Yes, sometimes you will still happen to win a Haneman with Honitsu Toitoi.
But that only means it worked out by chance.
More often, you simply miss the win.
Avoid this kind of call that turns your own hand into a bad shape.
Example 5
Pon 
In Example 5, if you call you can reach tenpai immediately.
But just because you can tenpai does not mean you should call on anything.
Pon 
Pon
This is the kind of "well, at least it tenpais" call.
But if one key tile is already used by another player, the hand is finished.
Pon 
Pon
This also looks like "the tile came out, so I called it."
But the point is that a tile from the player on your left can be chii'd.
Chi Pon
That matters, so I will say it twice:
do not call on everything.
Original Japanese page: http://beginners.biz/naki/naki10.html