Wash once before first use. It sets the loop and takes out the small amount of lint every new towel has.
Warm water. Tumble dry low. That is the whole method.
No fabric softener. No dryer sheets. Both work by leaving a thin waxy film on the fibre, which is exactly what makes laundry feel slippery, and a film that repels water is the last thing you want on a towel. If your towels have stopped drying you, this is usually why.
Skip the bleach too. It weakens long-staple cotton faster than anything else in the cupboard.
At 800 GSM these need real air. A crowded radiator will not do it, and a towel that stays damp is a towel that starts to smell. Give it a rail with space around it and it hangs dry in a few hours.