One of the biggest mistakes I see in Holdem amongst armature poker players is over playing seemingly good hands when they are either marginal hands or should be mucked.
Time and time again I see hands like AQ offsuit and KQ offsuit over played. Don't get me wrong these hands are very powerful starting hands when played in the right circumstances, but many players lose big time on these sorts of hands when they are clearly out gunned.
Let me give you an example.
You have AQ offsuit in a middle position
Assume that the players on this table are of average standard unless otherwise stated.
The player under the gun calls and a good player behind him raises. You must understand that there is a very good possibility you could be up against two hands that are better starting hands than yours. If you are up against AK, which is the mostly likely starting hand that is better than yours, you are drawing to just your queen or an unlikely straight as your outs. Worse still you could be up against pocket queens, kings or aces. Furthermore, there are a number of players behind still to act that may have hands better than yours or have good drawing hands that can draw you out, remember AQ off does not play as well in large pots. The correct play here is to just fold. You would also fold hands like KQ off and QJ off. If you have suited connectors you may consider playing them, particularly if a few loose players at the back might call. Remember, with suited connectors you want a large pot with many players, because these type of hands play well in large pots.
Another bad scenario is to have a hand and like KQ offsuit up against a hand with an ace in it heads up. Particularly, AK or AQ. Often if someone raises from early position with these types of hands and you call with KQ you will end up heads up or possibly against two opponents. This is a sucker play, because even if you hit your card you don't know where you stand after the flop. If you miss your flop you are almost certainly beaten.
I often see players who will call three bets with hands like AQ off. This sort of play is suicide, because you can be fairly confident you don't have the best starting hand with little chance of drawing to the best hand.
So the conclusion is beware of calling raises with hands like AQ and KQ off suite. Particularly, if the raises come from average to good players.