Yes, use your trip odometer, to measure how far you've gone on a tank of gas. You also have a reserve switch on the left side of the fuel tank, near the seat. Make sure you switch that to ON when you fill your tank. Ride around town till it stalls out on you, then switch to reserve, and ride to the nearest gas station. Check how many miles you put on till you hit reserve. You know then at what mileage you hit reserve, so start looking for gas before that.
Also, practise switching the fuel switch while riding. Sit in your driveway, on the bike, and practice reaching around your leg and switching it. I ride a zx-7r also. To reach my fuel switch, I stick my left knee out a little, and reach inside my knee to the switch. Practise it with your gloves on too. Its an important thing to be able to do on the freeway, in heavy traffic, without missing a beat.
I usually start looking for gas at around 100 miles on the odometer. I know I have a little more room then that, but its not worth risking it. I think mine gets 120 miles before I have to switch to reserve, then another 20 miles on reserve, for a total range of 140 miles. Mine is jetted, and is running a full Yosh exhaust. When my bike was stock, I got about 140 miles before reserve, then another 30 miles on reserve.
Keep it shiny Side up.