From sequence. Lead high from any sequence. The only exception is AK on a trump contract. There are too many situations, where it is necessary to lead by A without K, so if you have both lead by K. If the partner do not know exactly where is the A, he should encourage only if he has Q. So if he does not encourage, he still can have J. This is a disadvantage of the method, but here any mehtod have its own disadvantages.
From long suit with a honour. On notrump contract I use standard fourth-best lead. On trump contract I use 3-5-lead convention. This means that you should lead the smallest from odd number of cards and third from even. The reason is that with this lead the partner more often can determine the exact length after the first trick which is often important (e.g. in cash-out situation). Notice that a small spot lead promisses a honour (usually AKQ or J). I hate attitude leads. Moreover, if you hold something like KJ92 and your partner can not guess your honour, lead 2. Count is usually less imortant than strength.
From short suit. Usual convention: high from a doubleton; and you probably know how to lead from a singleton.
From collection of spots. I use MUD (middle-up-down) for odd card suit and lead high from even, although there are two situations where I do not like to do this. First, if my second-high is sufficiently small (e.g. I hold 842), especially on notrump contract, I lead high and then put middle. It is more dangerous to show a honour which I do not have than to decieve in count. Moreover, sometimes your partner will be able to notice that a small card is hidden and compute the count (however, this is a kind of a psychological game with declearer). Second, suppose I want to lead from 4 card suit but my top spot may be useful for getting a trick. Then I lead second high and then put the smallest.
Signal preference. Encourgment, count, suit preference (Lavintal signal).
Inverted signals. Small spot means encouragment and eveness. Be sure that your spot is sufficiently high when you want partner to switch or to show the odd count. Do not play middle, a declearer does not have to play cards in ascending order!
Italian discards. Odd spot means strength in the discarded suit. Even spot signals suit preference. If you discard an odd, especially on a notrump contract, then you usually show a stopper rather than very strong suit (if you can hope to establish the suit, why should you discard a trick?).
Playing by honours. When you cover you usually play the lowest card from a sequence. If you play by unnecessary honour (e.g. partner led by king or dummy played by ace and you play jack) this honour is the highest fom a sequence (your jack promisses 10 and denies queen). The same applies when you discard a honour.