It's always best to use good quality solid vegetable shortening when greasing your pans. In the past, I would just use a folded paper towel to apply the grease. Then I moved on to a brand new, never previously used, 2 inch wide paint brush. I used that brush specifically for greasing pans. My latest discovery are the silicone pastry brushes.
Even though mine is a chef with a silicone brush head, it still works great.