Ask friends who have been to Thailand to book hotels in Thailand online. Do they need to print the reservation form themselves? Do I need to pay a deposit when I check into the hotel?

You don't need to print the reservation form, just report the name of the reservation person at the front desk. Hotels in Thailand generally need to pay a deposit, but it also depends on whether you use a credit room or a flash room as a deposit guarantee when you book online. If you do, you don't have to pay the deposit at the front desk. If you don't, you need it.