How do I find the "sweet spot" on a lens?

I've heard people talk about this many times but, how does one determine it? I was thinking some small print and just try different focal lengths & stops? Any help much appreciated.
Thanks,

Yep, try it and see, preferably on a tripod and of the same thing for each shot.

Thanks Tim, I'll give it a try then.

Boy, everytime I get a new "toy" I try to do a comparison to other lenses by shooting a sheet of newspaper stuck to the wall outside. Trouble is, the resluts doing this do not agree with the pictures I get later. Maybe you should test your lens under acutal conditions and see what it does best (at what settings, etc.) I think diff. people who work diff. ways would report diff. answers.

So I just went through this with a new Tamron I just bought. In this case I was looking for color reproduction, contracts, Depth of Field, and sharpness. Basically I choose three seperate subjects, and shoot a series of shots from a tripode starting at wide open and then moving down two stops until I have gone through the whole range. In this case it is a 28-75, so I did the same test at 28, 50 and then 75. Works out to be beween 20 and 30 shots per location on each subject covering the focal range. Try to do 3 very different subjects. I shot some flowers, my AC unit (boring but has a good grid pattern) and an old barn. In this case, the sweet spot for this lense starts at f6 and extends to f11. Below and above that you don't get maximum contrast. Thats what I do... may not be right - but works and now I know.