Safe Winners
Not every card that wins is worth the same. Some tricks are locked in the moment you lead them: no defender can touch them, so the only question left is how much you can bank while you're at it.
Read the official rule on what wins a trick.
Your Ace of Spades leads, and the Ten follows right behind it: two winners cashed back to back, and nothing anyone holds can get in the way.
The guaranteed winner
A card is a safe winner once nothing outstanding can beat it: the last trump still out, or the top card of a suit every remaining player can still follow. Lead it and the trick is yours before anyone plays a card.
Winning cheaply
When you're the one deciding a trick you're already going to win, there's no reason to spend more than you have to. Play the lowest card that still beats what's on the table and save your strong cards for later.
When every card wins
Late in the round, sometimes every card left in your hand is a guaranteed winner: the highest trump, the top of every remaining suit. Lead your highest-point card first: order stops mattering once nothing can stop you, so bank the biggest tricks while you're picking.
Doppelläufer
Hold the Ace and Ten of the same suit with nobody able to head them off, and you have a Doppelläufer: cash the Ace first, then the Ten follows for free next trick. Two winners for the price of one lead.
Near the top, late in the hand
You don't always need the actual highest card. Once most of a suit's higher cards are already out, a card that's merely close to the top is safe enough to lead: check that a defender can't be void first, or you're handing them a free ruff.