When You Have Two or More Dora
When your hand already contains two or more dora, it is a chance hand.
You should aim for the shortest path to winning.
Do Not Get Greedy
Example 1
Pon 
Pon 
Dora
In Example 1, if you discard ,
you can make Toitoi, Haku, Chun, and Dora 2 for a guaranteed haneman.
But that is too greedy.
Even if you discard , the hand is still mangan, and the number of waiting tiles doubles.
Turning a mangan ryanmen wait into a haneman shanpon or kanchan is a loss.
Example 2
Dora
This is a Menhon Dora 3 hand that is already guaranteed to be haneman.
If you draw 
here,
☆ Tsumo
rather than discarding and making baiman (Menhon Ittsuu Dora 3),
discard and take the 
wait instead. The bigger the hand, the more you should pursue winning ease.
Also, if someone discards from the original Example 2, just pon it and discard .
☆ Pon 
Your precious menzen honitsu drops to mangan,
but the hand now waits on . When the dora are in a concealed triplet, it is better to take the wider wait even if the value drops a little.
Example 3
Dora
If the dora were not ,
discarding to aim for 234 Sanshoku would not be a bad idea.
But when the dora form a concealed triplet,
discard and aim straight for tenpai.
If your upper player discards a callable tile, take chi-ten immediately.
If the hand is still mangan after calling, there is no reason to pass.
☆ Chi 
Build the Hand with Calling in Mind
When you have Dora 2 or Dora 3, even an open hand is still worth plenty, so it is important to play with the attitude that calling is the natural thing to do.
Example 4
Tsumo 
Dora
Suppose you are dealt this starting hand in the South round.
The only tile you should cut is .
Lock in the two dora and aim for Tanyao Dora 2, or a 3900 hand by pairing a value tile.
This is exactly the kind of hand where the value-tile “express ticket” matters a lot.
Example 5
Tsumo Dora
With Dora 2, you should break the pair and head for open Tanyao.
Rather than discarding or and dragging the hand out as a closed hand,
an openable Tanyao is simply faster.
Theory Summary
When your hand contains two or more dora, prioritize speed and winning ease.
You should build the hand on the assumption that you are willing to call.
Original Japanese page: http://beginners.biz/dora/dora03.html