When deciding to come in over an opponent's opening bid, the general guideline is:
On the 1-Level:
Takeout Double = Opening bid strength (if <18, then at least 3 cards in each unbid suit)
Overcall in a suit = 5+ cards, 8+ HCP on 1 level (better suit/strength if 2-level overcall)
Overcall of 1NT=15-18 Balanced, their suit stopped
On the 2+ Level:
Takeout Double = A little more, the higher the level
Overcall in a suit = 5+ decent cards and opening-bid strength
2NT overcall = 15-18 Balanced, their suit stopped
3NT overcall = "Natural" -- wide range, wide number of possible hand types (their suit stopped)
With both sides vulnerable, RHO deals and opens 1. What is your call holding:
AQ765
KJ65
2
Q32
Pass
Double
1
Other
With neither side vulnerable, RHO deals and opens 2. What is your call holding:
KJ2
QJ5
KJ876
Q2
Pass
Double
2NT
3
Other
With both sides vulnerable, RHO deals and opens 3. What is your call holding:
KQJ1092
KJ65
A
A2
Pass
Double
3
Other
You are vulnerable against not. RHO deals and opens 1. What is your call holding:
Q765
KJ6
KJ4
AJ2
Pass
Double
1NT
Other
With both sides vulnerable, RHO deals and opens 3. What is your call holding:
J7
KJ6
AKQ1076
K2
Pass
Double
3NT
4
With neither side vulnerable, RHO deals and opens 1, what is your call holding:
K3
KQ2
K94
J7652?
Pass
Double
2
With neither side vulnerable, RHO deals and opens 3. What is your call holding:
KQ95
K2
AJ10
K1098?
Pass
Double
3NT
Other