ax+by=1 form transformations

Hi,

I'm doing some power studying, so yep, I'm going to be posting a lot of questions. I was just wondering, how do the values of a and b affect the equation ax+by=1? I've Googled some stuff and haven't found any basic list of rules. The only thing I have found (from a practice test and answer key) is that if a>0 and b>0, then the line will have a negative slope and not pass through the 3rd quadrant. Any other rules that I should know about?

Haha, the Pre-Algebra stuff went right out the window, as you can tell (up until this point in my life I've had Pre-Alg, Alg 1, Geometry, then just finished Alg II this past year). :P

Thanks!

imcq