1) As usual one needs solid agreements. If one partner bids 5NT as pick-a-slam, and the other takes it as grand-slam-force, one can easily lose 16 IMPs.
2) With quite a weak hand, either preempt quite high or be quiet.
To illustrate the issues around 2, imagine one is playing weak-twos in the range of 5 to 8. Now the opponents can get into the auction and often end in 3NT, knowing:
- the weak two bidder cannot have a good suit and an outside entry - either the suit is not good enough to establish, or the hand has no outside entry to get in to run the suit once it is set up
- the location of values is fairly well marked for declarer.
- the weak two bidder side likely does not have the values to penalize the opponents if they step in.
Contrast these considerations if the "weak-two" is, say 8 to 11 in range. Now the factors are not so tilted against the "weak" side.
So with the quite-weak hands, one is usually better off pushing the bidding to a higher level, or staying quiet to not provide the opponents a roadmap to play the hand. I've seen this theme repeated time and time again watching this past week. Opening at the three level with the quite-weak hands at least takes some exploration room away from the opponents, though can drive them to 3NT for better or worse.
For the Euro championships it's been magnificent coverage by the Polish organizers.
Also today the US team trials started. A very strong field as usual and will be fun to follow the results.