River Betting
A very easy place to lose money is in the river betting round. People bet without winners and that's the equivalent of simply throwing their money away. What's different about the river is that there are no more cards to come. Because of this you have to adjust your betting to accommodate the fact that your hand can no longer improve. The question you should always ask yourself is this: Do I have the winner? Backtrack through the hand and observe your opponents' betting pattern. This will often make what can be a tough question to answer much easier.
You should only bet on the river for two reasons: to attempt to steal the pot with a bluff or to gain value (value bet) with a sure-fire winner (or at least a hand you are 75% confident is the winner). All other questionable marginal hands should be checked. The reason is this: let's say you decide to bet on the river with a questionable winner. What can your opponent call with? Your opponent also realizes that there are no more cards to come that can improve his hand, so if he was on a draw, he will fold. If he senses any strength in your hand and he feels he doesn't have the cards to play back, he will fold. He will probably fold if you have the lead in the hand and he has less than top pair, good kicker. When will he call or (even worse) raise? When he has a winner. There's no other legitimate hand that an adept poker player could have that would merit a call on the river. It's that simple.
What constitutes a 75% sure winner or whatever other threshold you feel comfortable with largely depends on the pace of the game and the board. If the board is not connected nor suited and the game is playing loose, top pair with any kicker may be good enough to win. In the same situation but with a tight game, you may need a strong kicker or even two-pair to take the pot. With a scarier board, the threshold may be a straight or a flush. Make sure you have these hands if you bet, otherwise check and either fold at the heat of a bet or hope have the cheapest showdown possible!
Reading straights before a showdown: a straight is a very misleading hand. A straight made with 3 to a flush on the board is threatened by a potential flush. A straight with a paired board is threatened by a full house. These are easy to see. What is less obvious is a straight going up against a higher straight. This is why you should rarely draw to the idiot end of a straight (the low end) if there is legitimate betting action. Someone very well may be drawing to a higher straight and complete it as you complete your idiot end straight. On the river, it is sometimes best to simply check/call with idiot end straights. On one hand, you do not want to release a straight. On the other hand, you want to minimize your losses when you do come across the higher straight.
Tricks to reading a straight: a simple trick to use when trying to read the strength of your straight is to check where your hole cards are being used in the straight. When using both your hole cards to make the straight, you have the nut straight (nut, assuming there is no flush or better out there) as long as one of your hold cards is not the tail end of the straight. If you are only using one hole card, you can never have the nut straight (unless it's Ace high) and should probably play in a check/fold mode when your one hole card used is the idiot end.
Detecting straights: one of the most common ways to complete a straight is with suited connectors. As such always be aware when two connecting cards would complete the straight. For example, a board that looked like QJ832 has a T9 gap. T9s is a very playable hand and under heavy betting you should probably fear the nut queen high straight. Naturally, straight boards with gaps in it such as QT832, pose significantly less of a threat since J9 is more likely to be folded than T9; the larger the gap the less of a threat the straight is. Of course, this depends on the player, but if your opponent is consistently playing J9, you should celebrate anyways!