Relax! Most vehicles can pass their smog check! First take care of any maintenance that is due (or overdue) such as an oil change or tune-up before the smog check. If you do mostly city driving, give the car a run on the freeway for 50 miles and fill up with a fresh tank of quality gas. Premium fuel can improve your odds slightly, and make sure your gas cap is intact and fits tightly. A visual inspection of the engine compartment could reveal broken or cracked hoses or components. Do those repairs before the test.
The Test-Only Smog Check, an essential part of the Smog Check II program recently initiated in the Bay area, is considered a more consumer friendly smog check and is no different from the smog performed at any other of the smog stations.