Gottfried Wilhelm Leibniz had several principles of philosophy and theology. Some of which are widely used and recognized today and perhaps some are ignored. The first, and perhaps best known, principle is the principle of sufficient reason (PSR). There are two forms of PSR: PSRa and PSRb. PSRa states that there must be some sufficient reason for why something exists rather than not. PSRb states that there must be some sufficient reason for any positive fact whatsoever. However, is PSR true in all possible worlds? This is highly debatable. Is it a metaphysical brute fact that any fact has an explanation? But wait, what’s the explanation of that PSR? Perhaps PSR, in the end, is question beggining.
Then there’s the principle of perfection: God always conducts himself in the most perfect manner (See Discourse on Metaphysics, Sec. 3, passim]. Thus, for Leibniz, If God creates then God creates the best possible world. By the way, possible world semantics were first used and developed by Leibniz. On a similar note, there is the principle of least action: God always chooses the most minimal means by which to produce the world or states of affairs, etc. This is akin the the simplicty to a virtuous theory. We often hear of a theory as beautiful, elegant, or simple.