Make sure that the province with the most/most advanced buildings is the one you want your new king to appear in. Nothing worse than being the English and finally taking Constantinople and you king dies and your new king appears there but you have no boats in the med. Instant rebellion in the north!

Don't ever retreat your king into a castle to wait for reinforcements. Did that once and 90% of my provinces rebelled. I would call that being stupid if I ever did it again.