This topic separates the amateurs from the experts.
There is no shortcut.
It takes lots of concentration and experience.
This article is intended only as a very brief introduction/summary
As declarer, here are the main things to focus on:
1) In a trump contract, always count the trump suit. The best method is not the "fingers method." In other words, don't count "1-2-3-4" for the trick you see in front of you and then add "5-6-7-8-9" adding the 5