Here's what I did:

Almost a week before the test, I ran a bottle of "Guaranteed to Pass" fuel additive to a full tank of gas, ran that tank through and filled up with a fresh tank the morning of the test. The wekend before, I replaced the air filter and changed the oil and oil filter. Don't know if that really helps, but it can't hurt. If your plugs haven't been changed since the last smog test, or you have no idea when they were last changed, put in a fresh set of standard single electrode Bosch plugs of the correct heat range. Check with your owner's manual or the dealer if you're not sure. Next, I disconnected the electric cooling fan plug near the A/C receiver/dryer, hopped on the freeway and drove about 5 mi. one way and then 5 mi. back at 65-70 mph, then sat outside the test facility and ran the engine at 2000-2500 rpm in neutral for about 15 min. till the temp gauge was up to about 100+ deg. C (it was a coolish day, but make sure you've got a full reservoir of fairly fresh coolant), then, without shutting it off, handed it over for testing. It passed with flying colors!

The trick seems to be to get that catalytic converter as hot as you can before the test is run, and try to keep it that way right up to the moment it's tested. If you do it during the cool part of the day, you can control the engine temp when running a high idle by just backing it off to about 1000 rpm, where the engine fan will cool it down a little.

DON'T FORGET to reconnect the cooling fan plug!

Hope this helps.

Gary