Washing the hair every 4 weeks is perfect, use a sulfate free shampoo when washing, do not scrub the hair! you want to gently pet the shampoo/conditioner on and gently wash out all shampoo and conditioner. Always let your wig/topper air dry completely before styling or brushing.
Argan oil is great for rubbing between your hands and running mid-ends of hair to keep it from getting dry since your hair piece is not receiving the same natural oils that our bio hair does. (my preferred brand is by OGX)
Silicone Mix can be used as a great deep conditioner for the hair pieces that can be done every 3-4 washes when you feel like the hair needs it. it really revives the piece.
If you use heat tools keep the heat at 300 degrees, to ensure longevity of your piece.