Obviously, you'll need to treat your Titan right if you want him to obey orders and do its job. Keep your Titan happy. Teach your Titan right and wrong with patience. Try to see it's own point of view. Discipline your Titan only in extreme conditions, and reward it whenever it does something right.
Self esteem is important.
Train your Titan constantly and without rest, keeping it fit for fighting as well as spell-casting. Your Titan is a resource for exploiting. Your personal slave. O.K., let's put some more detail into this, starting with the first rules. A Good God's top priority is to keep it's Titan happy.