As Jim says, the light in your area will greatly effect how you see ISS. I have seen it perhaps 50 times over the last couple of years. I live in a very high light suburban area. When it comes over on a clear nite, however, anything above about 45 degrees, it will appear as the brightest thing in the sky. It looks like a very intense landing lite on an airliner--once it gets over 45 degrees.
The times to see it best are in the predawn and just after sunset. If you use one of the general sat tracking programs like Orbitron, Nova, or similar, watch for passes where it is dark for you on the ground--you are on the dark side of the terminator, and the ISS is still illuminated. This will be on passes where it goes over you within 1/2 hour or so of sunrise or sunset, generally.
One of the neatest things I've ever seen in the sky was the 90 degree elevation pass of ISS and the Shuttle in tandem.
Good luck and have fun.
Curt KU8L