Over time, you can get a few different sizes (.490, .495., .50), some different thicknesses of patch, different lube, and try different sizes of charge/powder grade (e.g., 3F or 2F; different brands, too). Just be careful with the size of your powder charge and don't increase increments too fast (no more than 5 grains at a time). Safety first, always.
Like any cartridge firearm, each one seems to have its preference on load. But a .490 PRB is a great place to start and seems to be what many (if not most) people stick with in a .50.