Emissions Test in Ontario

a number of things....warming up the car (heating up the cat) makes it more effective, running the car at the correct temperature (make sure that they put a fan in front of the rad, etc.) or else the car will run hot and the ecu will pull timing (running rich)

clean injectors will help also of course.

+1 on warming up the car fully. You should take for a few wide open throttle runs on the highway before bringing it in to the test centre.

Run a bottle of Chevron's Techron Fuel Injector cleaner a couple of tanks BEFORE taking the car in for testing. FI cleaner will burn off the deposits and you do not want it in your exhaust while testing.

Like others said, make sure car is nice and hot, so catalitic converter operates efficiently. Fill up with good gas.

Something else to think about: when was the last time you had a tune-up? You can change spark-plugs and sparkwires yourself. While you are at it, change a distributor cap too. All can be done under $100.