Being on lead has its advantages and disadvantages. The fact that you start the ball rolling by leading your suit to take tricks is a plus, but the minus is that you must choose your card before you seee dummy! It's often difficult to find the right lead to beat a contract, but here are some guidelines if you're wondering what to lead:
Decide first, which suit to lead, and then which card of that suit is the right one.
Nobody makes the correct lead all the time, but thinking about the bidding and imagining what dummy might look like will help. In no trumps your goal is usually to develop your long suit, using either promotion, length or the finesse. Declarer is using the same techniques too, but the defenders can't see each others' cards, so it doesn't always appear to be the same thing. Timing is important and the defenders are one step ahead of declarer because they got to make that openinge lead.
The level of the contract you're defending might influence your lead. Defending 1NT is different to 3NT, which again is different to 6NT. Against 1NT and 3NT you might lead your long suit, hoping to establish it after giving declarer a trick or two, to which they are entitled. But against 6NT, it would be dangerous to lead away from any honour you're holding (e.g. fourth highest of your longest and strongest) because that might just be the twelfth trick declarer was looking for. So, make a neutral lead against 6NT, unless you know you can't beat the contact in another way. (e.g. ♠9863 ♥Q1065 ♦86 ♣K107). Lead the ♠9, rather than a heart or a club. You give away nothing this way.
- If partner has bid, lead their suit unless you have a good reason not to.
- Generally leading your own long suit is best. Lead the top of a sequence. You're using promotion here.
- Lead fourth highest of your longest and strongest suit, (if you don't have a sequence at the top) You're using length here.
- Lead suits that have not been bid by declarer or dummy
If it’s your own suit, lead the:
- Top card of a sequence or a near sequence of three or more. From ♠KQJ52 or ♠KQ1054 lead ♠K. With ♠KQ432 lead ♠3
- Top card of an interior sequence, with ♠KJ1085 lead ♠J
- Fourth best if no sequence, with ♠K8753 lead ♠5.
- Low from three cards to an honour, with ♠Q72 lead the ♠2
- Top card of a doubleton, with ♠106 lead the ♠10
- It's fine to lead away from an Ace when defending no trumps e.g. ♠A864. Lead 4th highest, ♠4
- With three small cards such as ♠973 lead low unless you have raised partner's suit in the bidding, when the 9 would be more helpful.
When, as third player, you see partner's lead, consider carefully which card to play. Your first job is to WIN the trick for your side, but if you can't, because the trick has already been won, the card you play will help partner.
eg partner leads ♦Q (from ♦QJ1085) and you have the ♦K7. You must unblock with your ♦K, because otherwise you'll be stuck winning the ♦K next, and won't have a small card to return to partner's long suit winners. You're not playing a high card unnecessarily, because partner will hold all the important cards underneath the ♦Q.
Work out when the correct card is fourth highest and when it should be top of a sequence. In no trumps, you need three touching or nearly three touching to lead the top, otherwise lead fourth highest.
In order to keep your defensive communications, it may be necessary not to take your winners first, but to let declarer win an early trick, so that you can win later tricks. e.g. holding ♠A10853 you lead fourth highest ♠5.Partner wins the ♠K, and returns one. It may be correct NOT to win your ♠A, but to duck a trick, ensuring that partner has a spade left to return to you later, when you are able to enjoy your last three spade winners. e.g. the situation may be this:
♠A10853 Partner ♠K72
(you lead ♠5)
It will work out best in the long run to make standard leads, because this will help partner know what you're holding, and then they will be able to work with you to beat the contract if it's possible.
Looking for more information? These books will help you learn the basic skills required to play bridge.