Face: Clean your face with soap and water, preferably something with antibacterial qualities. A clean face is important, as you'll be rolling needles through your skin, puncturing it, which allows foreign objects like bacteria to more easily enter.
Dermaroller: If you see any skin or other superficial debris like blood, rinse under warm water for a few seconds to remove. Disinfect the dermaroller by fully submerging it in 60-90% rubbing alcohol or hydrogen peroxide for 10-15 minutes (under 60% isn’t enough to properly sanitize). Allow dermaroller to completely dry before using.
For other methods to clean see this site. Isopropyl alcohol is the cheapest and will work.