Opening bid - 1NT  

To open 1NT you should try to ensure that you have some control in all suits by having an honor card in each. Notrump openings show a balanced hand and can be made with a five-card major suit or a five-card minor suit. You should also have an honor card of Queen or higher in all of the suits and your hand should not contain a void , a singleton or a worthless doubleton .
Distribution of your hand can be in either of the three following patterns
5, 3, 3, 2
or
4, 3, 3, 3
or
4, 4, 3, 2
If your cards are in either of these three patterns your hand is called "balanced" or "flat".

* If you have a 4 card major then your partner can use the Stayman Convention (2C) to discover them.          

Opening with a 1NT Bid · 15-17 HCP · a balanced hand · No more than 1 doubleton* (2 cards) · Your hand may contain a 5 card major suit · Your hand may contain a 5 card minor suit

*Note

A doubleton when in a NoTrump contract should contain an honor card with the rank of Queen or higher. If the doubleton has two cards neither of which is a Q or higher then it is referred to as a "worthless doubleton" because effectively there are no stoppers in that suit