In our modern times, cars are an essential part of life just like food and shelter, and with our national economy such as it is, everybody is trying to keep their cars longer.
Well when this happens and your car gets older, there are some things about your car’s maintenance you are going to have to become aware of.
One of those things is
when you have to go and get a smog test for your car. Until your car is officially seven years old, a majority of people won’t think about it.
But be warned, if you do fail the smog check, what was supposed to be a small $50 smog check suddenly turns into a huge auto repair bill.
When you need your vehicle to pass a smog test so you can renew your vehicle registration. Here are some tips you can take so your inexpensive smog test, can pass with flying colors.

First, be positive that your vehicle is running correctly. If your vehicle is not running correctly, get it to an auto service shop as soon as possible so they can see if their is a problem.Then have it repaired before your smog check.

Second, an easy but necessary tip, take a drive. Remember
passing the smog test means your car needs to burn fuel efficiently with as little or no smog emissions a possible. Well when your car is not properly warmed up, it may not have proper combustion. If that happens, you stand a chance of failing. Just take it for a drive for 15 minutes or so and you will get your car to run optimally when it is taken in.

Third,
add fuel additives. This you do when you are filling your auto up with gas. You just put it into the gas tank. What this does is it
helps lowers emission levels by cleaning your car’s intake and exhaust paths.This gives the fuel and air the ability to flow freely.

Fourth,
have your tires inflated to the proper pressure. This little known tip helps your car drive more smoothly and more accurately during the smog check.This greatlly improves the emission overall output because
it helps the engine maintain a steady load.

Finallly,
change your oil. If your engine oil needs to be changed and is contaminated,
this could very well cause you to fail your smog test. Contaminated oils are high in hydrocarbons and that could cause the failed test.
Follow this guidlelines and tips and you are going to have a good chance of passing the smog check with flying colors.
Source: http://www.whichengagementrings.com/unc ... -smog-testMore about the Smog Test:
When a Smog Inspection is RequiredCurrently,
smog inspections are required for all vehicles except diesel powered vehicles, electric, natural gas powered vehicles over 14,000 lbs, hybrids, motorcycles, trailers, or vehicles 1975 and older.
Vehicles registered in areas subject to the biennial smog certification program are required to submit evidence of a smog certification every other renewal period. Owners of vehicles six or less model years old will pay an annual smog abatement fee for the first six registration years instead of being required to provide a biennial smog certification. The registration renewal notice mailed to you by the department will indicate if a smog certification is required. If a smog certification is required and you have not had a smog inspection, you may still pay your registration fees to avoid any late fees. However, you will not receive your new registration or year sticker until the smog information has been received by DMV.
NOTE: Upon initial registration, nonresident and specially constructed vehicles 1976 and newer require smog certification. The six or less model years old rule does not apply to these vehicles.
When you transfer a vehicle that is four or less model years old a smog certification is not required. (Determine the oldest-qualifying year model by subtracting three from the current year.) A smog transfer fee will be collected from the new owner. When a vehicle is more than four model years old, a seller must provide evidence of a current smog certification except when one of the following occurs:
The transfer occurs between a spouse, domestic partner, sibling, child, parent, grandparent, or grandchild.
A biennial smog certification was submitted to DMV within 90 days prior to the vehicle transfer date (a vehicle inspection report may be required for proof of certification).Smog certifications are good for 90 days from the date of issuance.
When a car is sold, who is responsible for the inspection?The seller is required to provide the buyer with a valid smog inspection certification at the time of the sale or transfer. Smog certifications are good for 90 days from the date of issuance.
The inspection is not required on a transfer if a biennial smog certification was submitted to DMV within 90 days prior to the vehicle transfer date (a vehicle inspection report may be required for proof of certification).
Note: Smog certifications are not required for transfers that occur for any motor vehicle that is four or less model years old. (Determine the oldest-qualifying year model by subtracting three from the current year.) A smog transfer fee will be collected from the new owner.
Does my vehicle qualify for a smog exemption?
Smog inspections are required unless your vehicle is: 
Hybrid

1975 year model or older

Diesel powered

Electric

Natural gas powered and has a Gross Vehicle Weight rating of 14,001 lbs. or more.

Motorcycle

Trailer