By the time you get to the river, or fifth street, even at a low limit game there will often be only two or three players left. Let's take a look at your options once you find yourself at the river.
Betting/Raising For Value
Value betting and raising are bets you put in the pot hoping to be called. You believe you have the best hand, and every bet in the pot is profit for you.
Deciding to call a bet on the end is pretty straight forward but it requires you to have some read on your opponents' hands. First, check your pot odds. Then, compare your pot odds to the estimated chance that your hand is good enough to win. If the odds against your hand winning are better than the pot odds, you call. Otherwise you can consider folding. If you're up against multiple opponents, you can take expected overcalls into account when figuring the pot odds - however you also have to take into account those other players' hands when deciding the strength of your own hand.
Often you won't know where you stand at the river. You think you're hand is pretty good but not a lock. All other things being equal, be more prone to call when the pots are large than when they are small. The reason for this is that when you call at a large pot, you have to be correct less often than when you call at a small pot because those large pots will make up for the times you're wrong and don't have the best hand.
The decision to overcall on the river depends on how likely you think your hand is to be good. The problem with overcalling is that not only do you have to beat the bettor but also the other callers.
If you are the last player to call, that is all you really need to take into account. However, if there are players left to act after you, the chance that they will raise will need to be taken into account as well when calculating your pot odds. This can get quite complicated with many players still in at the river.
Finally, if you find yourself holding a lock hand with many players at the river, you need to decide whether your overcall would be more profitable than a raise.
For instance, there are 5 players at the river. The first player bets, the next player calls and it's to you. If you expect the two players behind you to call as well, then a call is in order as that one bet will earn four bets. However, if you think that one or both players behind you might fold for the single bet, then a raise is in order; since the two players behind you will be folding anyway, you can collect two bets from the original bettor and caller. Often someone who has put in a single bet on the river will call a single bet as well.
You must have a good hand to overcall and the more callers between you and the bettor the better your hand must be.
Bluffing on the river in limit hold'em can be tricky business. The problem is that the pots are often large enough that an observant opponent will call if she has any chance of taking down the pot. An unobservant opponent will often call to "keep you honest" rather than because pot odds dictate it. Occasionally you will find a weak opponent who is willing to save a bet on the river by folding to your bet; after all, "a bet saved is a bet earned" - or at least that's what you'd like him to think.
The usual river bluffs occur when you believe your opponent was on a draw and you believe she missed. Another instance where a bluff can pay off is when the board pairs on the river and you've been aggressive throughout the hand.
In order to be confident your bluff will work, you need to have some reads on the playing styles of your opponents. If you're facing a calling station, a bluff will almost never work. Against an aggressive and tight opponent, a bluff can work if he doesn't seem to be paying attention to pot odds when making plays. A play who seems to be scared money is also more likely to fold to your aggression on the end.
How do you decide whether to call on the river with a marginal hand? How do you know you aren't being bluffed? After all, you'll often arrive at the river with a hand you can't really be sure is a winner. Well, we start by taking a look at the pot.
How many best are in the pot? How many bets to we have to call to showdown? Those are the pot odds. As an example, let's say there are 5 big bets in the pot, we're heads up, and the player before us has bet, so it's one bet to us for pot odds of 5:1. Our hand is a marginal third pair with top kicker. A scare card came on the river, as well. The bet could be a bluff.
But what do we compare our pot odds to? We don't compare it to the chances against making our hand because our hand is made - and we're not too thrilled with it. Rather, we compare the pot odds to whether we think our opponent is bluffing. If she bluffs a lot, then we might think she's definitely bluff more than 1 time in 6 (5:1) and it's worth a single bet to win 5 bets. However, if she is a player known to bluff very little, less than 1 time in 6 for sure, then you can save the bet and fold.
If you have no read, it's tougher. You have to keep in mind that if you call the bluff you'll win 5 bets for your 1 bet. That's a great win. If you fold, then you've given up those 5 bets for just a single bet. Mathematically, that's a bit of a disaster. The larger the pot, the more you should be willing to call a single bet on the river when you have any chance of winning.
Inducing A Bluff
If you find yourself at the river with a strong hand against an aggressive opponent, you might try to induce a bluff. You induce a bluff, if you are first to act, by checking your good hand and hoping a later player will bet, allowing you to raise. The downside of this play is that your opponent(s) may check and you never have the opportunity to bet.
So, why try to induce a bluff? Why not just bet? When you successfully induce a bluff you can sometimes win an extra bet when, had you bet out, your opponent would have just folded. Additionally, you might be able to win another extra bet if your opponent actually had a weak holding and calls your raise.
Again, inducing a bluff is a double edged sword. If you read your opponent as weak or passive, then this play can backfire when she checks behind you.