Use a well draining soil that is designed for containers. No dirt or top soil or garden soil. Mediums with less peat are better typically. If you have trouble finding a good well draining soil, you could purchase a bag of Perlite to mix into the soil before transplanting. If your plant is root bound, you should try to spread the roots out and probably rinse out as much of the old medium as possible prior to transplanting. Give it good water to start with and don't expose it to too much sun for a few days after transplanting. I suggest at least a 5 gallon pot. Mixing in some slow release fertilizer might be good....such as Osmocote.
Bruce

Thanks Bruce! Im very excited. Ill be taking a trip to Lowe's tomorrow :)

Get some Happy Frog Jump Start and add it to the mix down by the roots. My nurseryman won't pot-up without it.

Here is a link that might be useful: Happy Frog Jump Start.