Fasteners should be 3/8” in from the edges of the riser into the tread. Fasteners should be driven straight in and not over-driven or under-driven, as that can affect the strength and holding power. Treads should have a minimum of 2 8d nails on each end of the tread into the stringer and riser and 12” o.c. across the leading edge of the tread into to the rider. There may be code or design requirements that must be followed.