Desert Safari is during the daytime, it will be hot and sunny so keep yourself hydrated all the time.
Wear sunglasses and hats and use sun-block to escape sunburn.  Male can wear anything practical and comfortable jeans, trousers or shorts with casual shirts or casual button-up shirts.  Women should wear something light and functional like jeans, trousers or a long skirt with a t-shirt, long top, or casual shirt. If you are not going to do a lot of activities like horse, camel, and quad riding then you can even wear an active dress or a jumpsuit.