Beginner and amateur players tend to make their biggest mistakes on the flop and river, so it's understandable that everyone wants to perfect their play for these situations. However, the turn gets ignored once again.
Due to these factors many players just try to "survive" the turn. They have little or unreliable knowledge and experience and they try get a hold of weaker opponents on the other streets. Let's see a few typical mistakes that are made on the turn.
Autocheck on the Turn
The most common mistake on the turn is the auto-check. I see this mistake mostly with players who play in a defensive style. The attached train of thought can be something like this, "I have a great hand. The flop hit my hand so I bet. Ooops, he's called. I'm pretty sure he has something too, so it's time to play wisely. He might be stronger than me, so I would rather check on the turn."
Obviously in many situations checking will be the best move after the turn, but not always. Let's see an everyday mistake:
You raise preflop from late position with K-Q offsuit. The big blind is the only player who calls. The flop is Q-9-2 with two spades. Your opponent checks, and because the flop hit your hand we continue with a 3/4 pot sized bet. The opponent calls and the turn is a 3 of clubs. Your opponent checks again, so it's your turn. Many players handle the turn too passively and they check. Is this correct?
Of course not. Our opponent's preflop call range contains many combinations which will be draws after the flop. These are the followings: many flush draws, any J-T, K-J, K-T, and sometimes J-8 and T-8. The opponent called on the flop, so there is a good chance he'll have any of the above listed hands.
It's not necessary to explain that we lose value if we check the turn, because he would probably call a large bet. In this case it's true that even a smaller sized bet will be better than checking.
Betting too big on the turn
Another typical mistake is the opposite of checking and that is betting too big on the turn.
You play the middle phase of an online multi-table tournament, and you have a healthy 40 big blind stack. Let's use the same hand and flop as in the previous example. You raise 2.5 big blinds with K-Q offsuit, and there is only one caller. The flop is the same, Q-9-2 with two spades. We are continuing with a 3bb bet, and our opponent calls. The turn is a blank 3, and villain checks again. The pot is currently 12.5 big blinds. What happens if you continue with a 10-12bb turn bet? However curious the opponent may be about what the river could be, he realizes that the information is too expensive for him, so he folds with a frown. Did we make a mistake? The answer is yes. In these situations our job is to give our opponent pot odds that look mathematically tempting, but really are not.
Overbet all-in on the turn
An extreme example of the too large bet on the turn is the overbet all-in. (An overbet is a bigger bet than the size of the pot). A classic example would be playing high pairs in this manner. Let's say we have pocket aces, so we definitely raise preflop. Let's say you have one caller, but this time he has position on you. The flop is K-J-7 rainbow. We c-bet 3/4 pot and our opponent calls. The turn is a blank 3, and we move all-in with for twice the pot size. What do you achieve with that move? Do you think that your opponent is in a tough spot? If you do, that's wrong, we've actually made his life easier. He'll call with all of his two pairs and sets, and fold all other hands. You forced him to fold all hands that you beat, and you also took the opportunity of bluffing away from your opponent.
As a summary we can say that you lose value with too passive or too aggressive turn plays. There are many small mistakes in poker where you lose value in the long-term. Making the wrong turn play causes you to lose significant amounts even in the span of a single hand, not only in the long term.
There's another important view I hold regarding turn play. If we realise that several mediocre players are the weakest on this street, it's going to be obvious that this is where we can get a pretty sizeable advantage if we're more experienced. It might be beneficial to spend a couple hours on improving and analyzing our turn play, as it'll certainly pay off.