Your opponent preempts and leads another suit, what does that usually imply?

You are correct, it is probably a singleton.

What if he leads his suit? Then he probably has a singleton trump, asking partner to return his own long suit if won so he can use his trump!

The two way finesse and the Drop!

Many times you have the following card combination:
K-J-10-9 in Hand and A-x-x-x in Dummy

You can play either opponent for the Queen. If you have no information from the bidding, lead the JACK from your hand. Your LHO does not know where the kings is, and with the queen “cover an honor with an honor”. However, if you lead the jack and your LHO play low smoothly, play the ace and then Finesse through your RHO.

You have J-x-x-x-x opposite A-Q-x

DO NOT lead the Jack, if covered you still have two losers. Lead low toward the A-Q, if it holds, then play your ACE, hoping the King will fall!