Some good ideas from the other responses, but if the simple tune-up items don't work, you could spend more than you paid for the car to get it to pass the smog test. Passing tailpipe emissions standards requires that a lot of complex interacting systems all be working properly. Also, if the engine is very high mileage and/or perhaps has leaking rings, valve guides, etc. you may never get it to pass. I don't mean to be pessimistic, just realistic, but you need to have a competent (and sympathetic) mechanic give it a good look and tell you what it needs. Maybe with that kind of detail the more experienced members of this BB can then help.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230F)