Table selection is perhaps the single most important skill in all of poker, as it can have an enormous effect on your win rate. As an example, let's take an exceptional $2/$4 6-max player with a mean win rate of 2 BB/100 hands. One day, he sits down at a table full of players who are equally skilled. What's his win rate now? Intuitively, we might assume that he'd break even—which might be true at a friendly home game. In most cases, there is also a rake, often around 5%. If each pot is around 3 BB, and the player wins his fair share of pots, then the cost of the rake is:
Our +2 BB/100 hands winning player has become a -2.5 BB/100 hands loser, simply by picking a table with equally skilled players. This illustrates three important points:
How do we pick the right table? First, you must know what kind of players you can beat. This returns to the fundamental question: what is your strategy against each type of player? Once you can answer that question, look for tables full of the types of players you know how to beat.
Ideally, you would always play a table full of players you can beat by a wide margin. In practice, most tables you encounter will have some decent players. With a rake and against decent players, your strategy must be to avoid them. Even if you have a slight edge, you lose money playing against them due to the rake. Therefore, you must play tighter whenever a decent player is in the pot.
In some cases, a certain mix of players will frustrate your strategy. For example, some players are too tight and can be beaten by frequently stealing their blinds. However, if a too-tight player is at a table with some loose players, you will not get many opportunities to steal the blinds.