We have seen the routines and tricks people try to use in hopes of
passing their smog check.  We will try to discuss some of them here.
Do gasoline additives work?
We tested some additives from
various manufacturers and we are
not convinced.  Some customers
believe "Guaranteed to Pass"
additive works.  We don't want to
smear any manufacturer's reputation,
but we need evidence.  
Would my car perform better on the test if I heat it up?
Yes and no.  It depends.  We seen some customers rev up their engines or
circle the neighborhood to keep their cars hot.  Some cars benefit from being
tested hot; some perform better cold or warm.  We don't have enough room to
discuss here.  Keep in mind, some transmissions get severe damage from
improper revving.  An Emission Specialists should know each make and
model's idiosyncrasies to assure each test is fair and to avoid damage to your
car.
Does gas octane improve emissions?
We have no proof that octane makes a difference.  We never had a customer,
that we know of, passed or failed because of octane.  Just go by manufacturer
recommendation.  Octane 87 is good enough for my Explorer.