Who Actually Leads
The player to the dealer's left leads, no matter who named trump and became the maker. Call from first seat and you lead; call from anywhere else and somebody else does. The dealer always plays last on the first trick, seeing all three cards before choosing, which makes dealing the most comfortable seat at the table and the hardest to attack.
Leading as the Maker
Lead trump. You called the suit because you held it, and a trump lead takes one out of each opponent who has any while your partner contributes what they have. Two rounds of that and the opposition is usually empty, which is when the rest of your trump starts winning on its own.
Which trump depends on whether you can clear the suit or only dent it. With the right bower, left bower, and ace, lead the right and keep going: nobody can stop three rounds. With the right bower and two low trump, the same lead wins the trick and may show you where the left bower is, but it will not clear everything. Treat that as information, not control.
Weaker trump wants the opposite order. Holding the left bower and two low, or three middling trump, lead low first. You cannot afford your best card to do the pulling, and a low lead still drags a trump out of anyone holding one while your higher card waits for the second round.
One hand type ignores all of this: the one that called on off-suit strength, with an ace, a single card in another suit, and almost no trump. Play the ace, then get rid of that single card at the first opportunity. Once you are void in its suit, the little trump you hold may still take a trick.
Leading as a Defender
If you have the lead you are sitting to the dealer's left, which pins down where the maker is. Only two seats are possible and they want different cards from you.
When the maker is the dealer, they sit to your right and play last on every trick you lead, so anything middling gets beaten cheaply. Lead an off-suit ace, the one card they cannot beat in that suit, and keep away from low trump: a dealer who picked up holds a trump they will happily spend to take the trick for free.
When the maker is the dealer's partner, they sit to your left and play second, so they have to commit ahead of your partner. That is the entire point of leading through strength, and a trump lead is at its best here. It forces out a real trump, often a bower, while your partner still gets to see it and go over the top.
Behind both cases the order of preference is the one set out in how to play defense: off-suit ace, then low trump, then low from your longest off-suit. Leading trump on reflex is the mistake to avoid. From a hand with one low trump and nothing else it is a gift, because the maker takes the trick and carries on pulling trump, which is what they wanted anyway.
What the Up-Card Left Behind
The up-card is the one card everybody saw, and what happened to it is worth reading.
A Jack turned down in round one is the most useful thing you will see all hand. It goes into the kitty and stays there, and it is the left bower of the other suit in its color. Anyone calling that color in round two is playing a suit missing one of its two top cards, so treat the right bower as the only big trump in the game.
An ace turned up and taken by the dealer tells you the dealer holds the ace of trump and plays behind you, so leading trump into that gives them the trick for nothing. It does not follow that the rest of their hand is strong: the dealer swaps their worst card for the up-card, which makes a pickup the cheapest call available to anyone.
A 9 or 10 ordered up runs the other way. Ordering a low card up hands the dealer a free trump, so nobody does it without real strength behind it, usually a bower and length. If your partner did it, lead trump and back them.
Reading the First Trick
Everyone tells you something on trick one whether they meant to or not. A maker who follows a trump lead with a low card probably does not hold both bowers. A defender who plays under a trump lead without trying to win it may be sitting on something higher. A partner who throws off on a trump lead had none to follow with, and you are on your own for the rest of the hand.
The first trick costs you the lead. The second is usually where the hand is decided.
See Also
How to call trump covers the bidding that puts you in one of these seats, and counting cards picks up where this leaves off, at trick two.