An opening bid of 1
is assumed to be 4+ cards. The only time 1 is opened with 3 cards is with the exact 4=4=3=2 pattern (4-4 in the majors, 3 diamonds, 2 clubs). A 1
opening shows at least three cards in the suit. With 3-3 in the minors, open 1. With 4-4 in the minors, I recommend 1. With 4 diamonds and 5 clubs, I occasionally open 1 to avoid a rebid problem. (For example, with: 
4
K J 2
A Q 8 7
Q J 6 5 4
, I'd open 1 so as to be able to rebid 2 over a likely 1 response. That is much better than opening 1 and later reversing, rebidding 1NT with a singleton, or repeating the clubs).
Inverted minors are used (click here for my simple and basic treatment). Inverted minors are on by a passed hand, but off over any interference.
Bypassing diamonds after 1 If the responder to 1 has a 4+ card major and also has diamonds (4+), he responds as follows:
With a weak hand, bypass the diamonds and show the major at once.
With a stronger hand, bid up-the-line.
"Weak" means that the responder might bid only one time (planning to pass opener's rebid). So, usually, any hand up to 11 or so points should show the major and skip the diamonds. With 12+, bid the diamonds first (especially with 5 or more diamonds). With, say, AQ98 and J432, I'd skip the diamonds no matter what my strength. Judgment should be used. Opener also bypasses majors after 1-1 and rebids 1NT with any flat 12-14. If opener's rebid (after 1-1) is 1-of-a major he is assumed not to have 12-14 balanced.
Note: After 1-1, opener will usually show 4 spades (even if he has a flattish minimum).
Notrump Responses I recommend a simple schedule of 1NT for 6-10, 2NT for 11-12 and 3NT for 13-15. As usual, there are arguments to do this differently, but this is easy to remember and good enough. These ranges are the same in or out of competition. Of course, there is no 1NT forcing (nor semi-forcing) after a minor-suit opening bid.
Jump-shift responses
A jump to the 3-level in a higher suit (for example, 1-3) is weak--something like QJ108765 and less than 6 HCP. (If you prefer to use it as a splinter bid, make sure to both agree). A jump to the 2-level (for example, 1-2) should, in my opinion NOT BE WEAK. However, in the 21st century, the majority of players use it as weak, and just to avoid an accident, I will reluctantly mark it as weak on the LC STANDARD convention card. This is a rare area of LC STANDARD where I am (against my best judgment) going with the masses. I'm afraid to mark it as something else--because if one partner studies this and the other doesn't, a disaster will likely occur. A jump to 3 after 1 is natural and invitational (see responses to MAJOR openings, where this treatment was described). All other jump-shift responses are marked further down the convention card (under "Other Conventional calls").
In Competition
After an overcall, a cue-bid shows a limit-raise or better [example: 1 (1) 2]. A Jump-raise is weak [example: 1 (1) 3]. Notrump bids retain the same range as without an overcall.
After a Double, Redouble is 10+ and 1-level responses are forcing one-round.
A jump-raise after a double is weak, while 2NT shows a limit-raise.
There is an option (see Upgrades) to use "flip-flop".
There is also an optional gadget (see Upgrades) to use a jump-transfer to 3NT.
One other potential upgrade/gadget is Reverse Flannery -- also listed on the gadget page.
For a complete LC Standard card and a prettier version of these articles, visit Bridge Winners
Additional reading:
What Should we Play
