Author: Larry Cohen
Date of publish: 09/29/2015
Level: Intermediate
Planning the play at notrump is very different from suit contracts. While at suits your thinking is more along "what will I lose," at notrump, it is what will I win.
Count your sure tricks (in both hands). You can take into account the opening lead. For example, if you have 
K2 and dummy has 43 and they lead a spade, you are sure to take a spade trick.
It is rare that you will find you have enough tricks for your contract. In, say, 3NT, you will typically see 5 or 6 or 7 sure tricks.
The next thought is "How do I get to 9?"
Which suit will I work on? Will I have to lose the lead (maybe knock out an ace or concede a trick and hope the suit breaks)? Maybe I can take a finesse. What happens if I lose the trick and the opponents get in? What is my stopper situation?
For example, in the aforementioned K2 opposite 43, suppose you are in 3NT with a spade lead. You cannot afford to lose the lead! The opponents will take enough spade tricks to set your contract. So, if you have a choice of a finesse (maybe 
1098 opposite AQJ76) or knock out the 
A (maybe KQJ108 opposite 932), which would it be? Since you can't let them in with the A, you would have to rely on the diamond finesse.
But, what if you had 2 stoppers in the suit they led? Then you could afford to knock out the ace.
Declarer must always consider the "race against time." Can I get to 9 before they get to 5 (in 3NT). Or, can I get to 7 before they get to 7 (in 1NT). Consider what happens when you lose the lead--what is your stopper situation.
This is just a brief summary of play in notrump. Full details are in Larry's 2016 book and 2017 DVD on the subject.
Larry's Webinar Series on Notrump Play and Suit Play 2021
