Easy answer - but a adwise difficult to follow...
DONT GO ALL IN UNLESS YOU HAVE THE NUT hand.
Biggest problem in tournament poker is getting married to a hand. And the term "I where ahead" does not count - only the result in the end.
Say you are holding QQ and flop shows J-9-8 rainbow... You think - I'm ahead.. Right?
You bet - and get reraised... and call.
Turn shows a Q... you move all in and get called... What do your opponent have???
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Even a top opponent with pocket 10 would reraise your bet preflop - knowing that he possible is "behind" at the time... But with an open end str + pocket pair + still 2 cards to come... Loads of outs.
What error did you do in this hand...`? Forgot to geep an eye on the possible outcome of the hand.
A bad player could even have played the same way with like K10 suited.
My advise is to stop this all in play - and use it only when you have a nut hand or close to that.
In the above example, I would surely NOT move all in, as I always (depending on the player of cause) expect the opposition to be a clever player. If he reraise me post flop - he must have something..!
I would have bet the same as I did post flop (the bet he reraised) - and see his reaction. You just MIGHT have the next card cheap, if he wanna trap you. At this point I would be SURE that he got a 10... and who knows,- you just MIGHT have a lucky draw on the river to make a full house.
GL with it.
PS... You should take a look at Roy Rounder's book "No limit hold'em secrets"
http://files.meetup.com/222128/NoLimitHoldemSecrets.pdf (Download and start reading from page 43)