Responses to 1NT

One of my pet hates is 'practice Stayman', where a hand with no interest in the majors has to start with Stayman in order to invite 3NT. It helps the defence too much, especially on the opening lead. I'd rather guess between pass and 3NT than do that. There's no need for it because usually the 2S and 2NT bids are assigned meanings that seldom provide any real benefit.

I would suggest the following structure of responses to 1NT:

2C Stayman, always has a major if balanced
2D/H Transfers
2S Range finder or weak with long minor or GF 3 suiter with both minors
2NT Both minors, either weak or GF
3C/D Natural invitational
3H/S Natural slam try 6+ suit

After 2C:
2C-2D-2H: Both majors weak
2C-2D-2S: 5S and 4H game interest but not forcing
2 any - 2NT: invitational
2 any - 3C/D: Natural GF 5+ suit may have no major.
2D-3H/S: strong major 3 suiter, 3H=C shortage, 3S=D shortage
2H/S - jump in a new suit is a splinter.
Other major (i.e. 2C-2H-2S or 2C-2S-3H) is slam try with 4 card support and no shortage).

After 2D/H:
New suit game forcing except 2D-2H-2S which is forcing to 2NT or 3H/S only
Transfer then jump (eg 2D-2H-3S/4C/4D) is a splinter (in support of own suit :). With 6+ major, slam interest and no shortage start with 3H/S over 1NT.
Superaccept in new suit by opener shows values, or 2NT with scattered values but I like to just bid three of responder's suit to avoid telling them anything. May superaccept with a good maximum and only three card support.

After 2S:
Opener bids 2NT with min and 3C with max, then:
3C/D - Signoff
3H/S - Three suiter showing shortage

After 2N:
Opener bids better minor and natural after that. 3H/S by 2NT bidder is a fragment not a real suit as minor three suiters start with 2S.

After 3C/D:
Opener will usually pass or bid 3NT. 3 of a suit implies a fit and willingness to play 4/5 of the minor if stoppers for NT are not there.

After 3H/S:
Cue bidding

I think this handles everything pretty well and is not much to remember. Information about declarer's hand is withheld where reasonably possible. All hand types are covered. One suiters start with transfer if a major or 2C if a minor. Major two suiters start with transfer and bid other suit. Minor two suiters start with 2NT. Major/minor 2 suiters start with transfer if 5 major and 2C if 4 major. Three suiters start with 2C if both majors and 2S with both minors.

If they double our 1NT

Suit bids show a five card or longer suit
Pass forces redouble and bids then show spades and the suit bid
Redouble shows a two suiter without spades. Opener bids best minor then natural.

The advantage of doing it this way is that the hands we are most likely to able to compete on are the ones where we have a 5-4 fit or a 4-4 spade fit. These are identified immediately to allow opener to act if there is further bidding. Despite their double the hand may still belong to us or we could gain from pushing them a level higher.

If they double in 4th seat (ie 1N-P-P-X-P-P) then redouble with one suiter and bid lowest suit with 2 suiter.

Use the same method if they double our 1NT overcall or natural 2NT overcall.