Yoga or meditation? Personally I start with meditation however I don't think it really matters which you do first….Yoga is also a form of meditation is it not?
Depending on the type of yoga, it generally incorporates meditation within. If you are looking for additional meditation opportunities try breathwork upon waking, or a bodyscan for sleep. Personally i keep my dedicated meditation as part of my bedtime ritual however i know others that have to meditate upon rising in the morning. Its totally up to you to find a way that fits.
I really do medetation first because then I can set my mind to my yoga and be awake so that during yoga I don't fall asleep and get and my stretches in.
I personally do my meditation before my yoga so I'm not very tense from stretching my body out. After yoga, I usually want to lay down and relax, but I can't do that if I'm meditating.