If it is new and hasn't been fired before, make sure you clean all of their grease out of the barrel before you shoot it as well.
If you are going to use store bought prelubed patches more than likely you'll need to be prepared to swab the bore between shots, as they don't do a real great job of keeping the fouling soft and reloading can get very difficult (swabbing every shot is usually the most accurate as well). Just pack some damp cleaning patches in your container of choice, T/C #13 bore cleaner or similiar work fine. Some people simply put a dry patch in their mouth and use spit. Speaking of reloading, be sure to mark your ramrod so that you can verify you are seating the PRB (patched round ball) on top of the powder every time. If there is much of a gap between the powder and PRB it is the same thing as firing with a blocked bore.
A .015 patch and .490 RB are a great place to start, but keep in mind that you may need to adjust your patch thickness if accuracy isn't there with that combo.
I use the same cleaning method as Oldtimr, store with oil, and use isopropyl to remove it before shooting like Cayugad said as well.