In all my tournaments my only saying has been “no set no bet”. This should be yours too. That is the same as saying that “if you don’t get a three of a kind, don’t bet”. It’s foolish you squander your chips to excite your opponents’ reaction. You need to see the opponents’ betting before. Your rule should be to check if your score is not improved yet and if you think you have not some good cards.
After the flop is dealt, to use a roulette slang, les jeux sont faits. In texas poker the flop is a critical phase. Only after it, you can realize if you or your opponents have a real advantage depending on how the betting rounds of preflop and flop went on. If you realize the cards in your hand are worse than your opponents’ cards, you shouldn’t wait to improve them in the following phases. The only exception to this rule (I suggest you to stamped it in your memory) is when the other opponents check until the end of the round inducing you not to bet. This behaviour should suggest the other players have not strong hands unless they’ve decided to adopt a Slow Play strategy even with a Full or a Flush (but this should be impossible when there are either a pair or 3 suited cards on the board).
Another mistake that should be avoid is to overestimate your cards, i.e. when you have a middle-value pair in your hand. So if there isn’t a tangible score in your holding after the flop phase, folding should be your best and wise move.
You always need to remember another element as well. The Kicker. It’s the all-important unpaired high card in a hand used to settle ties. For instance, suppose there are two players, X and Y. If player X holds an Ace and a King and player Y holds an Ace and a Ten, they both pair the Ace but X wins because he has a higher kicker (King vs. Ten).
To conclude, I want to reassure an beginner player telling him or her that folding is the bravest move to act when you realize your holding is not strong enough. In fact, acting in that way, you could avoid to waste all your chips in vain, giving them to your opponents. Even a skilled player with an high pair in his hand decides to fold if he realizes one of his opponents could hold a higher score.
So you can tell a skilled player from an beginner one only if he acts in that way. As a matter of fact, beginners usually act upon curiosity and their curiosity can cost them too much!