Drying wet hair can cause brittleness and roughness, as it absorbs moisture and swells outermost cells. Heat treatment accelerates water evaporation, causing cell contraction and damage.
Never over-dry your hair
Since heat treatment on a daily basis is not a very healthy thing to do, so refrain from over-drying your hair to avoid its permanent damage.
Never use the same towel repititively
Use a gentle, microfibred towel to dry hair, avoid vigorous rubbing, and avoid rough towels that can damage hair irreversibly.
Never dry your hair all at once
Dry hair section-wise to prevent multiple strand drying, as moisture transports from wet to dry strands, damaging them.