[manudude03]

The 2 worst bidding mistakes when it comes to bidding:
Not using the system on normal hands (I've had 2 instances of people bidding 1NT-2S showing an 11 point invite with a 2443 shape or so- playing weak nt both times obviously)
Using blackwood when you don't know where you belong or how high even opposite the response(s). Had a hand recently where partner launched into blackwood when we could literally have belonged in any strain. Naturally, the wrong strain got chosen.

[Mbodell]

wank, on 2011-November-23, 02:28, said:

that type of psyche is ridiculous and pointless. the opps know you've psyched now, but you've also let them know about partner's hand. and if you had a 'long club suit' you could just pre-
empt to the 3 level directly instead of taking a circuitous route to a pre-empt at the 2 level.
if you're going to do this kind of thing, you have to follow it through and rebid 2M to limit your hand and shut partner up and prepare to go minus a large multiple of 50.

It isn't quite as bad as you make it out to be. For one thing, only one opponent gets to act after the pass, and if that opponent doesn't act it is over. For another, the opponents need to guess which is the psyche/misbid: the opening bid or the final pass. We've all likely either made this mistake, or witnessed this mistake, where one partner makes a game or slam try (drury, splinter, bergen raise, keycard, etc.) the other partner decides to decline the try but passes, rather than correcting back to trump. It isn't always revealing a psyche, it is just as often a mistake that was a slip of the mind. So the opponents don't know for sure.

[Yu18772]

jerdonald, on 2011-November-19, 23:31, said:

Not taking enough time to think about partner's bids.
Not analyzing the opening lead.
Forgetting the trump count.
Loosing trump control.
Take a finesse when there is a possible endplay.
Not watching your partners discards.

"Worst mistakes" depend on the level of a player, and thus expectation. I wouldn't "Take a finesse when there is a possible endplay" as the worst mistake a beginner can make. In general, the worst mistakes I seen (and made) at the table by new players are (no particular order).Play:

• Counting and combining information from bidding into play
• Jumping with an A on every occasion
• Not planning the play/defense at trick one, and not considering alternatives to a chosen line.
• Being "cheap" - not ruffing high (allowing unnecessary overruff) or not covering an honor when finessed etc....
• Signaling - either ignoring or over-interpreting partners signals
• Tempo in playing when finessed
• Ignoring scoring system

Bidding:

• Bid the same values twice - by far the worst problem of beginners imo
• Passing a forcing bid
• Not thinking about the next bid
• Learning too many conventions too soon
• Having no logic - memorizing rather than understanding bidding
• Ignoring vulnerability

Partnership and general mistakes:

• Not discussing hands and bids with partner
• Assuming that bad result on a particular hand is partnership fault
• Not discussing bidding enough in occasional partnerships, before the tournament
• Reading too few or too advanced books, without covering the basics first
• Not moving on to the next hand
• Not concentrating

I think that advanced/intermediate players suffer from another set of common mistakes, and some expert players from yet another......Also to be fair, to correct these takes a lot of time and practice, and in many cases these mistakes reflect a poor introductory teaching.

[Oof Arted]

sitting down at table in the first place

[32519]

I often see newcomers to bridge executing the "Elvis Coup" with monotonous frequency. E.g. As declarer you hold Kx in a side suit. LHO holds the AQx over you. To your immense relief LHO leads the Ace. The King is no longer dead. The "Elvis Coup" has given declarer a free trick.