First of all you'll have to really enjoy cooking, obviously. Chefs are generally on their feet for the majority of the time they are working and it is not unusual for them to have to lift heavy objects. Pots, pans, bags of ingredients, etc. that can be very heavy. You will need a knowledge of cooking and food preparation techniques as well as food safety to make sure that you don't make people sick with your food.
In a busy kitchen, you will need to know how to multitask, many orders may be coming in at a time.