First and foremost begin with cleansing, i.e. clean the area where the altar is to be set up. This should face the eastern direction if possible. You and others who will participate in the performance of the Puja should bathe, and wear clean and comfortable clothes.
Men may wear kurta/pajama combination, or dhoti/uttareeyam combination with or without a kurta/shirt/jibba etc. If men wearing dhoti decide to wear no upper garment, then a yagnopavita should be worn.