Avoid drinking a lot of caffeine before your session, especially if you've had a cup or two of tea/coffee through the day. We say so because caffeine is dehydrating, thus it isn't a great choice before performing Yoga.
Also, never eat a big meal before your session. A full stomach would make it difficult for you to get into Yoga poses. Hence, eat light.
After a sweaty Yoga session, don't uncork a wine bottle or grab a pint of beer. Because if you end up doing so, you are risking yourself for dehydration, which might bring along mild to severe headaches.
Also, avoid indulging in your love for sugars. And even if you're going to have some, make sure it's unrefined sugar such as an oatmeal.