I need help. I never know how I should be cropping my photos, as in what ratio.

I hardly ever print my images, but if I do choose to do so, what aspect ratio should I crop them in for just in case events? I usually crop my photos using the originals ratio, but sometimes that just isn't good enough.

So what do you think about when you crop, as far as dimension ratios? Or do you even worry about it? Should I just not worry about it, and reedit the original when I need to print it, and set it up for whatever size I am going to print it at?

Any advice on this topic would be GREATLY appreciated.