Fold-wise, I'd suggest Googling "angel wing fold". It's probably the most commonly-used fold for prefolds, and is my personal favorite. If the diaper is too long as-is, just fold the back in a few inches, then proceed with the angel wing or your fold of choice. Some will tell you to fold the front in rather than the back, and that certainly works too, though it can complicate pinning and leave you with an uncomfortable bulge in front.
When pinning, strive to keep the entry and exit holes on the outside of the diaper as close together as possible. You should be able to slide the pin back and forth once it's fastened. If you can't, then the holes are too far apart, and the pin might pop open under strain. Particularly if you intend to be active while wearing diapers, a good pinning job is important. I find that baby-sized diaper pins work just fine, but some have an easier time with the larger pins. The only trouble with the larger pins is that they tend to be on the dull side.