A couple more tweaks to what I'd said...
The 45 degree angle is about right -- any more "open" and you won't be able to get your left arm under the rifle.
Allowing your elbow/upper arm to rest against your chest gives you direct skeletal support from your arm to the ground (you don't want to muscle the gun). It will feel like you have twisted your elbow forward in order to get it to line up UNDER the gun; you don't want it off on an angle or you'll be muscling the gun rather than using your skeleton. With practice, this tends to be far more accurate than supporting the gun with your arm held out in front of you. Wrist should be straight. How you support the rifle (flat hand facing forward,thumb down, or on your fingers and thumb with fingers forward, thumb back, or with your fingers bent back, or even resting the rifle in the soft webbing between your palm and thumb, either palm forward or backward -- there are all sorts of positions that will give your rifle slightly different elevations, but your wrist should be straight). In any case, your point of support will be much closer to the action than you may be used to if you hold this way.
Lifting your right arm will raise the rear end of the rifle. If you don't, you will likely lower your head to meet the sights/scope. Raise your right elbow as high as you need to to get your eye lined with the sight/scope without creeping up the stock (otherwise you can get hit in the face -- though getting hit is much harder to do shooting in the 45 degree open position).
This leaves your right arm to pull the rifle into your shoulder (you don't want it loose). You have to do this while maintaining good trigger control.
Dan