How do I decide what color squares to place my pawns on? I often hear people say "I have my pawns on the dark/light squares like I'm supposed to" or something similar. I have no idea what actually dictates which squares to try to place your pawns though. Does it depend on the bishops the opponent has or doesn't have or is it more in relation to the opponents pawn structure? Or is it something else completely?
This is a very complicated subject since there are a lot of other factors that come into play so I will give some examples, but there are no general rules that apply in all circumstances.

First, let's take this common opening structure from the Slav. In this equal position, black wanted in imbalance, and traded off the light-squared bishop, so in order to keep some control of the light squares, he played e6. In addition to wanting to keep some control of the light squares, it also does not contribute to potentially making the Bf8 bad later.

 [FEN ""]

 1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. e3 Bg4 5. h3 Bxf3 6. Qxf3 e6


Next, lets talk about an endgame position with a bishop versus a knight or a same-colored bishop. In general, you do not want to put pawns on the same color of the bishop as that makes the bishop "bad". A bad bishop lacks scope due to its own pawns, and in addition, it often leads to zugswang.

Here is a position that is equal, but one bad move putting a pawn on the same color as the bishop, and it is over. In addition to limiting the Bf8, it weakened the light squares, and in many positions, it might have given white another target to attack.

 [FEN "5b2/3kpp2/1p1p4/5P2/3K2P1/1PP3B1/8/8 b - - 0 0"]

 1... f6 $4 2. Kd5 Bh6 3. Bf2 Kc7 4. c4 Bf4 5. Ke6 Kd8 6. Bxb6+


An exception might be if all the pawns are compact, and you want a draw. Consider this position where black plays e5, but then can put the king on the unassailable e6 square. Even losing f6 here would lead to a draw.

 [FEN "8/4k3/4pp2/8/4P2B/2b2P2/8/5K2 b - - 0 1"]

 1... e5 2. Ke2 Ke6


Next, let's talk about opposite colored bishops. In general, if you are winning, you want your pawns on the opposite color as your bishop, but often if you are worse, it is fine to put the pawns on the same color as the bishop since they cannot be attacked by two pieces.

Note in this ending how white advances the pawns, but always only when they can both stay on the light squares.

 [FEN "8/8/3k4/1b6/3PP3/4K3/8/4B3 w - - 0 0"]

 1. Bb4+ Ke6 2. d5+ Ke5 3. Bc3+ Kd6 4. Kd4 Be2 5. e5+ Kd7 6. e6+ Ke7 7. Ke5 Kd8 8. d6 Bb5 9. Ba5+ Ke8 10. Kd5 Ba4 11. Kc5 Kf8 12. d7 {and queens}


This last one is an example of the latter type discussed above. Black is worse, and has multiple ways to draw, but the immediate f5 makes it virtually impossible for white to win, let alone attack any of the black pawns. At best, they will trade some, and black will sacrifice the bishop for the last pawn.

 [FEN "8/4kp2/2b1p3/8/8/4B1P1/3KPP2/8 b - - 0 1"]

 1... f5


Summing up, and these are VERY general rules, most of the time, you want the pawns on the opposite color of your bishop, or if you are going to trade a bishop, trade the one that is of the same color as most of your pawns. Occasionally, you may find positions where you are worse, but the bishop can defend everything well if the pawns are on the same color, especially in opposite-colored-bishop endings, but if they are not opposite colored, you must look out for positions that are ripe for zugswang, so be VERY careful breaking the first rule about putting them opposite your bishop.

Lastly, in opposite-colored-bishop endings, if you are winning, keep them on the opposite color of your bishop, or they will be easily blockaded, but if you are worse, and trying to draw, often you can create a fortress by putting them on the same color as the bishop.