Do you intend to use a tarp over you or not? In winter I always take a tarp / poncho with me, as it really adds to the comfort factor if it is bucketing down.
It also gives you an "admin" area where you can store your gear and brew up etc in the dry.
If not taking a tarp, and you expect rain, take a dry bag that is large enough to put your rucksac in.
Routines wise, I sometimes pack my sleeping bag inside the bivy bag. That way, when I arrive I just give it a shake, slide in my Thermarest, and that's me set up.
I always get changed to go to sleep these days. Even if you think you are dry, you are usually damp, and this can lead to a cold, restless night.
If it is expected to go below freezing point, put your water bottle inside the bivvy bag.
Arrange / position your rucksac so that you can reach it in the morning. That way, you can make a brew without getting out of you doss bag.
Finally, sleep with your hat on!
Animadvertistine, ubicumque stes, fumum recta in faciem ferri
(Ever noticed how wherever you stand, the smoke goes right into your face?)