To become a good declarer

Learn and remember the standard plays
Play of card-combinations, Double-finesse,hold up, Blanko-Coup, Endplay, Squeeze, Percentage-play

Count, count, count ...................................
Your tricks, opponents tricks, Opponents points, opponents distribution

Try to imagine the lay of the cards from bidding, former play and counts.

If you are in a bad contract assume the cards are distributed as you need them to win.

If you are in a contract, that seems very easy, be cautious and assume the cards are laying against you and think how to overcome the badest distribution.