As per Hindu Scripture, Tulsi has a boon thatLord Vishnu accepts offerings only when they are first offer to Tulsi
First you should present the Tulsi mala to Lord Vishnu before wearing it. It should be then purified with Gangajal and Panch Gavya and let it dry before wearing it .
The wearer of Tulsi Mala should not eat Tamasik food like non-veg food,onion and , Garlic. He should also avoid alcohol, smoking and gambling.
The one who wear mala should be clean both mentally and physically as it is a sacred mala.
Devotees must note that wearing someone else's mala is also prohibited.
Devotes should maintain Celibacy and do not make physical contact with anyone while wearing Tulsi Mala.