One common area for misunderstandings are those sequences where one person pulls 2NT at some stage in the auction to a suit at the three level - is this merely trying to find a better partscore, or is it forcing? For example, try the following (all uncontested):
The last one you ought to know - going via the fourth suit and then bidding again is generally agreed to be forcing (see Newsletter 15).
Some of these sequences are standard, whilst others are merely a matter of agreement. The first clearly should be non-forcing, simply showing a hand too weak to respond at the two level. The second probably sounds non-forcing, so perhaps it should be for that reason. The third is clearly useful when you simply wish to play in 3♠, but most people play this as forcing, helping to reach the right game. Sequence four is a classic - it should be weak, simply showing 5-5 if you would open 1♠ on such a hand.
This is all very well, but trying to learn every different sequence is a difficult business, and there are plenty more. Can we find some sensible rule that agrees with one's intuition in the simple cases, but can also be applied to the more obscure situations?
* Pulling 2NT is forcing unless the hand is already limited, when it is non-forcing.
Note that this fits in with our decision on auctions 1, 3 and 5. For example, in 1, the 1NT bid limited responder's hand, so now the 3♣ bid is non forcing. We can also apply the rule to sequences such as 1♥-2♣-2♥-2♠-2NT-3♣. Responder is unlimited, thus the 3♣ bid is forcing. Not everybody would agree with this one, but it is surely better to know what the bid means than not?
* New suits are forcing unless the hand is already limited.
* Old suits are forcing only if supporting partner for the first time.
Note that these rules tie in to our comments above on 2 and 4. More generally, consider the sequences below.
Sequence A is forcing, as opener has not limited his hand (2♥ was forcing). Sequence B is forcing as opener is supporting partner for the first time (showing 5431 shape, trying to find the right game, or possibly slam). The last sequence is non forcing - suggesting only three spades and good clubs.
There is a sequence that some people would take issue with: 1♥-2♣-2♦-2NT-3♥. To many this sounds weak, and the above rule would suggest this is so. However, there is a considerable body of people who think this sequence ought to be forcing. With a weak hand and extra hearts you would simply rebid 2♥, hence the hand must have extras now, and simply be looking for the right game.
These rules are not set in stone, and will quite possibly not be the rules for you - think up your own ones. But if you want a serious partnership, then having a rule is a useful thing.