Every trump contract hides a small magic trick. You hold a loser you cannot get rid of, a card that looks destined to fall to the defenders, and then you trump it. Gone. One of their winners becomes one of yours.
Most players learn this move early. What far fewer players fully absorb is where the ruff has to happen to actually earn you a trick. Ruffing feels productive whenever you do it. It is not always productive. And the difference between a ruff that gains and a ruff that gains nothing is one of the biggest gaps between a casual declarer and a good one.
The trick you already had
Say spades are trumps. You hold five of them in your hand: ace, king, queen, and two small. Dummy has two little spades. Between the two hands you own seven of the top trumps, and you are going to make five trump tricks no matter what, because those five in your hand are all winners on their own.
Now suppose you ruff a heart in your hand with one of those small spades. Feels great. You just won a trick with a card that was going to win anyway. You have not gained a thing. Your five trump tricks are still five trump tricks. The ruff was free entertainment, nothing more.
This is the part that trips people up. Ruffing in your long trump hand, the hand that was always going to make its trumps by force, usually adds nothing to your total.
Ruff in the short hand instead
Turn it around. Ruff a heart in dummy, the hand with only two trumps. Those two little trumps were never going to score on their own; your long hand would draw them into the same tricks. But if dummy trumps a side-suit loser before those trumps get absorbed, that ruff is a genuine extra trick. You have manufactured a winner out of a card that had no future.
Here is the rule worth carving into memory: ruffs in the short trump hand tend to gain tricks; ruffs in the long trump hand usually do not. When you are looking for that one extra trick, you look at the short hand.
Concrete version. You are in four spades. Dummy holds two spades and a doubleton club. You have three losing clubs in hand. Play a club, play another, and now dummy is out. The third club? You lead it and ruff in dummy. That trump, which was going nowhere, just took a trick you did not otherwise have. Do it while you still can.
Why timing decides everything
The catch is that dummy needs to still have a trump left when you want to ruff, and it needs to be void in the side suit at the right moment. Both of those depend on the order you do things.
Beginners draw trumps first, out of habit, because someone told them to. Sometimes that is exactly right. But if you pull all the trumps and dummy has none left, you just threw away the very ruffs you needed. This is why experienced players will delay drawing trumps when they have short-hand ruffs to take. Set them up first. Draw later, if at all.
It also means you have to see the ruff coming before you play to trick one. Count your losers. Ask where each extra trick is going to come from. A short-suit ruff spotted at trick one is a trick in the bank; the same ruff noticed at trick eight is often a trick already lost to careless trump play. This is the whole argument for planning before you touch a card.
When the ruff is not there
Not every hand offers one. If dummy's side suits are all long, there may be nothing to ruff. If you are short on entries to dummy, you may not be able to reach the ruff even when it exists. And occasionally the safe line is to draw trumps and give up on the extra trick entirely, because chasing a ruff risks an overruff or a trump promotion for the defense.
Good declarer play is not "always ruff in dummy." It is knowing the difference between a ruff that pays and a ruff that just feels nice.
The trick you can only see in hindsight
Here is the frustrating thing about ruffs. You can play a whole hand, make your contract, and never know you left a trick on the table. Making four spades feels like a success. But if the deal was cold for five, and everyone else who held your cards found the short-hand ruff that you missed, you did not actually play it well. You just survived it.
That gap between "I made it" and "I made the most of it" is invisible at your own table. It only shows up in comparison. Tools like Bridge@Home let a full table play pre-dealt hands and then measure their results against everyone else who held the same cards, so a missed ruff stops being a secret. You find out the extra trick was there. Next time you go looking for it.
The takeaway
Before you ruff, ask one question: which hand am I trumping in, and were those trumps going to score anyway? Ruff in the long hand and you are usually spending a trick you already owned. Ruff in the short hand and you are minting a new one. Plan for it early, protect dummy's trumps, and half the extra tricks in bridge will start showing up in your column.