Could you give an example position? It's too tough to talk about chess in general terms.
Question about Silman's Reassess Your Chess

I think what he means is if there is an imbalance on a particular side of the board then that's the side you should play on and from that imbalance you should develop your plan. If there is more than one imbalance then you have to try and decide on which is the best one to work on. Trying to work on more than one plan at once is useless so choosing a plan is as important as having one in the first place.
Hope this helps,
A

khpa21 - Maybe your opponent has an isolated pawn, you have superior minor pieces, and you have more space.
AMcHarg - Thanks so much. Do you think Silman could have meant that if you don't have an imbalance anywhere, THEN you start playing on one side of the board? Also, what happens if you have NO imbalance? Like in the opening? Do you just create an imbalance?
You make a plan off of a combination of your imbalances and your opponent's imbalances. Say your opponent has a weak center but a strong kingside, and you have a weak kingside and strong center. Than you would want to play to exploit the weak center.
At least thats what this low rated player got out of it!

Thanks for your input wbbaxterbones.
Anyways, I found the answers to my question: 1) Like AmcHarg said, you CHOOSE a plan or imbalance to play on. 2) Like AmcHarg said, (again), You play on the part of the baord where a favorable imbalance exists. 3) It's impossible to have a game with no imbalances.
There. Done. Thanks so much, everybody.

To try to answer your question: first off, sometimes you're choosing between a few equally good plans, in this case it should be based on your tastes or if you want a safe plan or a dangerous but risky one. But to decide which imbalances are the most important you have to see which ones tactically give your opponent the quickest problems that he has to react to, giving you the initiative, which ones are the hardest to counter (for example if you play in the center as opposed to the kingside you wouldn't have to fear a central counterattack, because that's where your pieces are playing!), lots of things. Also decide which plans are more urgent than others. For example, you may want to build on the queenside, but you have a tactical chance to provoke a nice weakness or get a new useful imbalance (say bishop for knight, which may improve your chances) then you may want to concentrate on that first. Oh, and you want your plans to be as FLEXIBLE as possible! You don't want to let your opponent know exactly what you will do until you have to to make progress, so a lot of times before commiting to a plan it's good to improve your pieces where they can potentially play on either side of the board, both of which the opponent would have to then be prepared for.
Chess is hard to talk about, because it always depends on the specific position and there are so many different positions you will come across. But what I listed above are some things to consider when choosing a plan, the rest you will get with lots of experience, because I had your same problem as I'm sure many did.
This is why I don't like Silman's middlegame books. They contain unrealistic advice like "always have a side to play on", "always create a fantasy position", and "never look at individual moves until you understand the imbalances in a position".
I would instead recommend Simple Chess by Michael Stean.

Sure there are no imbalances at the very start of a game, that's what the opening is for... to create one. (See below):
Queen's Gambit. Black has an important choice already and he has only played one move! Does he accept the Gambit and be ahead in material (probably temporarily), or does he try to continue his central hold. White's plan is simply to sac a pawn for central control and initiative. As you can see, very quickly the game has imbalances that you want to exploit. Whenever there are no imbalances you need to try to think how you can create some in your favour.
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I've been reading Silman's Reassess Your Chess and it's great so far, but there are some confusing parts that I would like to clarify.
It says to play according to the imbalances. I understand that part, but what if there's more than 1 imbalance? What if there's three? How do you know which one to base your plan on? Also, what if you have 4 possible plans to choose from? How do you know which one to choose?
it also says that you should 1) Figure out all the imbalances in the position 2) Figure out which side of the board you wish to play on. Do you play on a side of the board during the opening / middlegame? Do you always HAVE to have a side of the board to play on? I don't quite understand it; how do I know whether to play on a side of the board or to play on an imbalance?
Thank you.