It is very important that your Audi Quattro be regularly maintained in order to pass the emissions test. Passing the emissions test requires you not to wait for a problem to develop in order to seek repairs. Instead, perform regular scheduled maintenance, oil changes, filter replacements, and so on.
Assuming at this point that your Audi has no emission related problems or apparent engine faults, to help the chances of pass a smog check you might want to consider getting a fresh change of oil (specially if you are not sure of when the last oil change was since you're the new owner), use new fuel, have the gas tank full between 1/4 and 3/4, and ensure the engine has been sufficiently warmed up before the smog test. In the unfortunate event your vehicle fails the smog test, the smog inspection report will offer some ideas of where the failure is at. A smog technician may then conduct a hands-on diagnosis to ascertain specific faults.
Things you can do to help your car pass the smog check.