Check your timing, change oil to name a few... I failed mine because I forgot to check my timing. It was at 14* and I failed miserably, ie. gross polluter . Now it's at 10* and I need to get it redone..good luck.
Clean the idle air bypass and the EGR valve with gummout. Remember to get new gaskets for both first. On timing -- they passed mine with 13* BTDC. I seem to recall reading that cheap 87 octane gas actually runs cleaner than premium. You could also try some alky or smog pass stuff in your gas tank. When you go for the test, be sure that the cats are HOT HOT HOT. Do some serious blasts just before to heat them up, and do not shut the motor down while you wait in line. If you ever thought about an h-pipe, now may be the time. Fresh cats make a huge difference. 2.5" high flow cat h-pipes flow almost as good as off road pipes, and new cats are probably the biggest thing you can do to clean up your act. Both of my '90 LX's pass test only, but the modded one with GT40 heads; E303 cam; MAC shorties; BBK h-pipe; MSD6A; and Flowmasters actually blows cleaner out the pipes than the stock motored car. I attribute the difference in large part to a relatively new cat h-pipe versus the stocker with 130k miles on it. Good luck.