No, don't worry, I'm not going to get all Segovia on you.  You don't need to buy a slide rule or a T-square to pinpoint exactly how you should sit.  But your posture is very important because if you are not comfortable, you will get tired and sore.  And that gets in the way of playing the oud, which we don't want to happen.
All you have to do is look at two or three master oud players, like Farid el Atrache, Yorgos Batzanos, or Serif Muhiddin Targan, and see that there was and is no set way of holding the oud.  For some pieces by Targan, I've found that I actually need to lean way over the oud so I can reach the high notes more quickly and easily.
But in general, you should follow these basic guidelines: 

     1.  Your back should be straight and your shoulders as even as possible.  Your right arm (if you're right-handed) should be coming to the strings starting just above the middle of the base of the oud.  This takes some time, and depending on the size of the oud and the size of you, it might not happen exactly like this.

     2.  The oud should not be leaning back or forward.  If you are sitting up straight and looking straight ahead, the face of the oud should be parallel with your face.  Also try to keep the length of the oud straight and parallel to the floor.  Over time you'll see that the round back fits snugly in the nook formed by your thigh and your abdomen.  You also shouldn't be supporting the neck with your left hand, the oud must 'sit on it's own.'

     3.  Have your right leg elevated to make the oud less of a stretch, which will help you keep your good posture.

Remember, there isn't really a set way of holding the oud, but if you follow the guidelines above and focus on being comfortable, you'll be just fine.

Copyright Mavrothi T. Kontanis. All rights reserved 2008