If you are unable to complete your state tax return by deadline (for most states, April 18, 2011), then you should file an extension before the tax filing deadline to avoid possible late penalties and fees.

Check your state's tax website to make sure you know what the deadline is.

State vary on tax laws -- in fact, Alaska, Florida, Nevada, South Dakota, Texas, Washington, and Wyoming dont' have any state income tax, so if you live in any of these states, you will not have to file a state return.http://www.taxfoundation.org/taxdata/show/228.html#state_individualincome_rates-20100327 

New Hampshire or Tennessee residents pay state income tax only if they have interest or dividends.http://retirementliving.com/RLtaxes.html

If your state does have a state income tax, then you can find out exactly how to file an extension there by visiting your state's Department of Revenue (DOR) website. The process of filing an extension varies from state to state, so the safest way to ensure that you comply with your state guidelines is to read the tax laws yourself.http://www.irs.gov/businesses/small/article/0,,id=99021,00.html

Some states require an extension form be filed, while others don't. If your state does not require you to file an application to extend your tax return deadline, then you can skip to Step 3.http://www.irs.gov/businesses/small/article/0,,id=99021,00.html

Now that you have examined your state tax laws, you will need to complete any forms that are required to file your extension. If you are also filing a federal tax extension, you might be able to forgo a state extension form if you attach a copy of your federal extension to your state return.http://www.irs.gov/pub/irs-pdf/f4868.pdf 

You can usually download a form on your state's DOR website. If you do not have access to the Internet, you can also pick up required forms at your local library. The makeup of the form will depend on your state, but generally you will need to provide the following information:

1. Your full name
2. Your current mailing address, including ZIP code
3. The type of state tax return you will be filing - either an individual return, a partnership return, a fiduciary return, or a corporate return
4. The date you need your deadline extended to - Usually the maximum you can request is six months.https://etax.dor.ga.gov/taxguide/TSD_Tax_Guide_for_Georgia_Citizens_2010.pdf 
   

You will also have to report the exact reason you need to file your extension. State DOR offices have the authority to deny an extension claim, and they may do so if your reason is not valid. Be sure that you only file an extension when it is truly necessary.https://etax.dor.ga.gov/taxguide/TSD_Tax_Guide_for_Georgia_Citizens_2010.pdf 

After you complete the form, make a few copies of it. You may need to submit multiple copies of the form to the state DOR. You should also keep a copy for your tax records.http://turbotax.intuit.com/support/iq/Print-and-Save/Save-a-Backup-Copy-of-Your-Tax-File/GEN12008.html

If you will have a balance due on your state return, filing a state tax extension does not give you additional time to pay your taxes owed. This means that interest and penalties will continue to accrue until you finish paying the balance in full.https://etax.dor.ga.gov/taxguide/TSD_Tax_Guide_for_Georgia_Citizens_2010.pdf 

To try to avoid this, it is best to pay your full balance before the tax deadline. Follow the payment instructions for your state tax return. You may be able to pay with a check, credit card, or debit card. If you are unable to pay all of your balance, send as much of it as you can with your extension form. You may also be able to establish a payment plan with your state.https://etax.dor.ga.gov/taxguide/TSD_Tax_Guide_for_Georgia_Citizens_2010.pdf 

The instructions included with your state form should include the mailing address to send your payment and forms to. Be sure to send off your forms by the state deadline to remain in compliance with the tax laws.https://etax.dor.ga.gov/taxguide/TSD_Tax_Guide_for_Georgia_Citizens_2010.pdf 

If your extension request is granted, you should begin preparing your tax return right away, so that you can complete your return as quickly as possible. This is especially advantageous if you are due a refund, since it will help you to receive your payment sooner. Consult a tax professional if you need assistance working on your return.https://etax.dor.ga.gov/taxguide/TSD_Tax_Guide_for_Georgia_Citizens_2010.pdf