Magic numbers:

Part score: 19-24 points
3NT / Major game: 25+
Minor game: 27+
Suit small slam: 31+
6NT: 33+
Suit grand slam: 35+
7NT: 37+

Opening:

Balanced hands (no void/singleton, <=1 doubleton): 
12-14: 1NT
15-17: 1 of a suit, rebid 1NT
18-19: 1 of a suit, rebit 2NT
20-22: 2NT
23-24: 2Club, then rebit 2NT

Unbalanced hands:
6-9, 7-card suit, poor defensive values: pre-emptive 3 (8-card suit: 4)
12-19 1 of longest suit [rule of 20: open if hcps and length of 2 longest suits>=20]
16-22, 8 playing tricks, 6-card suit or at least 5-4 two-suiter: 2D,H,S,
23+ 2Club (forcing to game)