Source: http://www.bridgebum.com/ 
Novices are taught a ‘count-and-classify’ approach to bidding: Count the points in your hand, look at its shape, and then Classify it as a specific bid. Balanced with 15-17 HCP? Open 1NT. 6 spades with 5-10 HCP? Open 2.
As novices get more experienced, they learn more elaborate rules. Bergen’s Rule of 20. The Law of Total Tricks. Losing Trick Count. Adding a point when holding all 4 aces. Subtracting a point with 4333 shape. Pearson Points.
I’d like to offer a more creative technique that comes in handy: envisioning specific cards in partner’s hand. For example, you hold:
| AQJT43 |
Q74 |
3 |
JT2 |
Partner deals and passes. RHO opens with 3, weak. Do you overcall 3? Novices struggle with this type of problem because there is no ‘count-and-classify’ rule for 3-level overcalls.
Here are my two cents, which I’ll give you for free. 🙂 In this scenario, imagine what cards that partner could hold. You’re allowed to be optimistic. (Try it.) How about 3-card spade support, the AK of hearts, and the queen of clubs? Something like this:
| xxx |
AKx |
xxxx |
Qxx |
Partner’s pass shows 11 HCP or less. The hypothetical hand above is a bit optimistic (spade support and fully-working face cards), but it only contains 9 HCP so it’s certainly possible. 3 is virtually cold. Even 4 has a chance if partner gets trigger-happy and raises you to game.
Might partner have 0 HCP, in which case 3 will go down several tricks doubled? Yes, but we have to deal with probabilities. RHO’s preempt shows 5-10 HCP, so let’s mark him with 8 HCP on average. If you hold 10 HCP, that leaves 22 HCP for partner and LHO. On average, they hold 11 HCP apiece. So while it’s possible that LHO holds 22 HCP and partner holds 0 HCP, it’s quite unlikely.
This technique may be difficult at first, because it requires playing out the hypothetical contract in your head. In the above example, you have to “see” in your mind’s eye that 4 relies on a spade finesse, which is 50-50 (maybe less due to RHO’s preempt).
When this hand came up at a local club game, 3 was passed out and made easily. Partner’s hand:
| 75 |
AJ |
9765 |
A8763 |
In short, don’t over-rely on rules and formulas for hand evaluation. There are times when it helps to imagine certain cards in partner’s hand, and bid accordingly.
– See more at: http://www.bridgebum.com/envisioning.php#sthash.CMuI0zYi.dpuf