The place to start is the charge you have been indicted on. Prior convictions weigh into criminal history, not the initial guideline range. If you have been indicted, you should talk to your lawyer about what the scenario is. You should understand that there are a lot of factor that go into determining a guideline range, some of which are not knowable early in the case. Also the court is to use the guidelines to calculate a sentence, but then decide the appropriate sentence which may or may not be in the guideline range. Get a good defense attorney, I have included a site that can give you an idea regarding the guidelines ranges.
This response does not create an attorney client relationship and is offered for informational purposes only. Only a lawyer fully versed on the facts and circumstances of your case can properly advise you on the case. I am licensed to practice in Minnesota, not every state. You should always consult with an attorney licensed in your area on how best to proceed.
Federal criminal defense lawyers spend hours pouring over the guidelines. Please do not try to figure these complicated rules out on your own. You need to consult your attorney. He or she should be willing to walk you through how they arrive at their guideline result.
Understand, big, thick books are written on the subject of how to apply the guidelines, and may appeal court case opinions have been written on the subject.
It's simply not one for the layman to take on.
Answers on Avvo are for general information purposes only and should not be relied upon as legal advice. No attorney / client relationship is created by providing this answer. For specific advice about your situation, you should consult a competent attorney of your choosing.