If I had to point at one factor that makes club duplicate less enjoyable that it should be, it would be players ignorant of Law 16B, which has to do with playing the game honestly. All bridge teachers and directors should make a concerted effort to teach Law 16B in a way that newer players can understand.
LAW 16 AUTHORIZED AND UNAUTHORIZED INFORMATION
B. Extraneous Information from Partner
1. (a) After a player makes available to his partner extraneous information that may suggest a call or play, as for example by a remark, a question, a reply to a question, an unexpected* alert or failure to alert, or by unmistakable hesitation, unwonted speed, special emphasis, tone, gesture, movement or mannerism, the partner may not choose from among logical alternatives one that could demonstrably have been suggested over another by the extraneous information.
(b) A logical alternative action is one that, among the class of players in question and using the methods of the partnership, would be given serious consideration by a signifcant proportion of such players, of whom it is judged some might select it.
2. When a player considers that an opponent has made such information available and that damage could well result, he may announce, unless prohibited by the Regulating Authority (which may require that the Director be called), that he reserves the right to summon the Director later. The opponents should summon the Director immediately if they dispute the fact that unauthorized information might have been conveyed.
3. When a player has substantial reason to believe that an opponent who had a logical alternative has chosen an action that could have been suggested by such information, he should summon the Director when play ends**. The Director shall assign an adjusted score (see Law 12C) if he considers that an infraction of law has resulted in an advantage for the offender.
* i.e., unexpected in relation to the basis of his action.
** It is not an infraction to call the Director earlier or later.
Opening 1NT with a Singleton Honor
It may now be legal but no one will ever convince me that it's good bridge or something to try out at a club game. It used to be considered a psyche and it's still a psyche if you consider the expectations of the vast majority of club players.
Psyching at a club game may get you a top but it's not even close to being worth the animosity it creates, particularly among newer players. If you must psyche, be very careful not to fall into a pattern because it consitutes a a private understanding. Even if you've never actually discussed it with your partner, having an advantage with respect to recognizing partner's psyches is cheating.
Non-Standard Leads and Signals Should be Announced
Players should be required to announce non-standard leads and carding conventions before play begins in any level of competition.
The leads in bold on the convention card can be considered standard except for the choice of ace or king from ace-king. The king used to be standard in the US but the ace (always popular in Europe) has become so common that it's no longer safe to assume either is standard.
Some time ago, there was a very well-known and highly-regarded New England partnership who used third and fifth best leads against notrump contracts. The theoretical advantage is debatable but the practical advantage was huge. Fourth-best leads were (and still are) so common that just about everyone fell victim to it once. Why don't more people use it today? My guess is that feels too much like cheating.
Even expert players forget to check the opponents' convention card in which case upside-down count and/or attitude and other follow-suit signals become a private understanding and can be a huge advantage when declarer bases a line of play on the opponents' carding. Lavinthal and odd-even discards have the same effect.
Odd-even discards are legal but odd-even follow-suit signals and encrypted signals are not. Upside-down count and/or attitude signals are legal but in my opinion, upside-down suit preference signals should be illegal. There's no theoretical advantage to them but using them to confuse declarer is a huge advantage.