The most important guideline about opening leads is to listen to the bidding!
Two cards touching each other constitutes a sequence. We lead the higher one of touching cards.
An important guideline is as follows:
1. Do not lead a singleton trump. You will help declarer find an adverse break in the trump suit.
2. Do not lead unsupported Aces (from spaces!) unless partner bid the suit or it is an unbid suit when they bid 3 suits looking to play in a NT contract. Aces are meant to capture Kings.