Back in the stone age it was sort of decided that a good leading strategy was to lead the fourth best of your longest and/or strongest suit. It is no longer the stone age. It is true that if you do decide to lead from a 4 card or longer suit HEADED BY AN HONOUR (!) then the 4th best card is the right card to play. But the crucial point is to decide whether or not that is the right SUIT to attack in the first place. The opening lead is probably one of the hardest parts of the game and many a contract will make or fail on the first card led. When the bidding is over you should all leave your bids on the table until the first lead is made. This is to enable the opening leader to look at and assess the auction while they opt for the - hopefully - correct lead. Here's a couple of hints:
1) Try not to lead a suit bid (or implied) by the opposition - especially declarer.
2) Try not to lead from an unsupported honour - especially A's or K's
3) DO lead the suit bid by your partner
4) Eliminate the suits you do not want to lead from and then choose the right card from suit you decide on.... but which is the right card, I hear you holler?
The standard approach is to lead: Top of a sequence (KQxx, QJxx, J1098 etc), top of an internal sequence (KJ109, Q109x), 4th best from an honour (Qxxxx, Kxxx) and 2nd from bad suits not headed by an honour (10xxxx, xxx), A from AK and top of a doubleton. Obviously singleton leads against a suit contract are always worth a shot as well. But you should not make one of these leads just because you hold them. These are the leads you make from any given holding once you have decided to lead that particular suit from your assessment of the auction. No amount of so-called "rules" will ever take the place of actually thinking about what to do in any given situation. "Rules" are not a substitute for thought. They are an aid to assist your thoughts in certain repeating patterns. On the other hand sometimes you're stuffed whatever you do. The auction goes:
1NT - 3NT. You're on lead with this:
Er.. I don't know either. Anything could be "right" or "wrong" but the rules state that you must lead something. But what? Frankly, I might choose a low card from one of the major suits on the basis that no-one bid a major, used Stayman or made a transfer, but if partner turns out to hold Qxxxx in the club suit I'm going to look a twat. Tuff. Score up, move on. Not an easy game is it?