I think strategy is used when you aren't sure things will go according to your plan. When you plan a house, you expect most of the problems and can be sure that your plan will overcome them. But in things like chess, there are lots of things that you can't be sure about or even expect, so you would use a strategy that is more flexible and less detailed. With a house you say exactly where everything will be, but you can't do that in chess!
strategy and plan

thank you ivandh.i forgot to tell you that im a writer.so the title of my story is buiding a house,so it seems that you agree that i cannot use the word strategy in the sentence if my story is about just buiding a house right?.so that means you agree too that you cannot use the word strategy in the sentence if their is no competition right? just answer yes or no in my question ivandh,thank you again...i wait to your answer.

* "Tactics is knowing what to do when there is something to do. Strategy is knowing what to do when there is nothing to do."

I think strategy is used when you aren't sure things will go according to your plan. When you plan a house, you expect most of the problems and can be sure that your plan will overcome them. But in things like chess, there are lots of things that you can't be sure about or even expect, so you would use a strategy that is more flexible and less detailed. With a house you say exactly where everything will be, but you can't do that in chess!
yeah i think your right ,thank you.

In terms of chess:
Tactics is the calculation of moves and the responses to moves. It the ability to look at the board and visualize "ok, I capture the pawn with my knight, he recaptures with his knight, i capture with my bishop, I'm up a pawn."
Strategy is general planning and positional factors that don't involved a specific sequence of moves or exchange of material. That could be a huge range of things, from looking a position and thinking "Ok, I have more space on the queen's side, perhaps I should attack there" to "the c5 square is supported by my pawn and can not be attacked by an enemy pawn, I really should get my knight there" to "I control this file, I should see if I can double or triple my heavy pieces on it and try for a breakthrough" to "his c6 pawn is weak, I should make it my target."
Strategy and tactics are always the right and left hand of chess. You need tactics to carry out your strategy once you have one, and playing by tactics alone with no real plan or positional concern will only take you so far.

That is it Bugobida. . .¡
Finally I have found a very good, clear, straight to the point definition of strategy and tactics.
There have been too many posts about the matter and bla bla bla without having clear in mind what is one thing and what the other.
This is your sentence:
* "Tactics is knowing what to do when there is something to do. Strategy is knowing what to do when there is nothing to do."
guys can you help me to know this?what is the difference between plan and strategy?can you used the word strategy in the sentence even though their is no compitition?,like for example i am building a house so i have no opponent,can i say what is my strategy of building my house?i think i cannot use the word strategy just buiding a house right.?