The answer really depends on which Chapter of Bankruptcy you previously filed (Chapter 7 and Chapter 13), and which Chapter you wish to file. Additionally, these restrictions only apply if you received a discharge in your previous filing.
Ch 13 -> Ch 13: You must wait at least 2 years after the filing of your initial case before you may refile and receive another discharge. Fortunately, more than likely you were in the first case for at least the 3 year minimum, so theoretically you could refile the day after you receive your discharge.
Ch 7 -> Ch 13: You must wait at least 4 years after the filing of your initial case before you may refile and receive another discharge.
Ch 13 -> Ch 7: You must wait at least 6 years after the filing of your initial case before you may refile and receive another discharge. There is an exception to this 6 year waiting period in instances where your initial Ch 13 was a 100% plan or where it was at least a 70% plan and proposed in good faith and your best efforts.
Ch 7 -> Ch 7: You must wait at least 8 years after the filing of your initial case before you may refile and receive another discharge.