How you keep focus?

Sometimes I play and I'm completely uncapable to focus on the game. When it happens I don't find out that I'm unfocused until I have lost a minute or a couple of minutes, and when I realize I lose focus again a couple of minutes later. Probably I'm not the only one, so, what do you do to keep your mind on the game??

Start less forum threads.

I'm not sure if you mean online or OTB game, however... I find it best to walk around and get some fresh air after a long think/when I am losing focus. 

Sometimes I play and I'm completely uncapable to focus on the game. When it happens I don't find out that I'm unfocused until I have lost a minute or a couple of minutes, and when I realize I lose focus again a couple of minutes later. Probably I'm not the only one, so, what do you do to keep your mind on the game??

Use less (or perhaps more) ganja.  Depends on the person.