Wow, some of you have really complicated pictures for envisioning time. For me, it's just like in a computer animation program...there's a left for back, or past, and a right for future. It moves in a horizontal line in front of me.
I will say, though, that I don't really orient the time scale around the present (for instance, by inserting my present self as the origin) but rather around whatever event it is that I'm thinking of. And when people say they're moving an event up or back a day, I have no problem understanding what they mean.