Platorepublic, et. al.
Descartes is definitely an awesome choice for practical application to one's own life. The inherent method laid out in Discourse on the Method
is very practical. Doubt, analyze down to the simplest component, reconstruct in a manner that is known to you as the most clear and distinct, and enumerate. Which is interesting in the respect that Descartes was thoroughly against the concept of the Aristotelian syllogism (a set of premises and a conclusion, etc.). In short, Descartes hated logic. He thought it hindered a persons natural train of thought from the "clear light of reason." And this is not a personal observation, but taken from Descartes' rage against dialectics (AT X 300-410: CSM I, 10-40).
Universal skepticism is definitely something that comes to mind in personal application. And especially within the context of the method in which we utilize universal doubt that Descartes posits in Discourse on the Method
, universal doubt becomes a very applicable subject. You have superficially a notion which has Descartes (and the reader) spinning around in a world of doubt. What really is certain in our own lives? This not only applies to the metaphysical dealings, but also to more abstract occurrences as well, like whether or not I am absolutely certain this may be the right job for me or that may not be the best course of action to take. Superficially, if you doubt that you have doubt about a given subject, perhaps it requires further examination. I think this is something many people could take to heart. An author and Cartesian commentator made a very interesting observation that the latter meditations on which universal doubt is founded are the actual necessary conditions in the first place, like a transposed Aristotelian notion of cause and effect.
There is fantastic quote from Descartes' unpublished work Search for Truth
(a must for the avid Descartes enthusiast) in which Eudoxus (Descartes figurehead), states, "Just give me your attention and I will conduct you further than you think. For from this universal doubt, as from a fixed and immovable point, I propose to derive the knowledge of God, of yourself and everything in this universetry now to show how these doubts can be used to prove God's existence
." (AT II 38-9: CSM K, 99)
But if you read Descartes the "right" way, you get some very good personal insight into his (and potentially your own) quest for knowledge. The notion of God (not to be misconstrued with religion or spirituality) was critical to him because it provided a fundamental basis to work off of. This applied to many rationalist that followed, like Spinoza and Leibniz. Cartesian philosophy seems to always come back in one way or another to the two primary theses of Descartes, God and the soul, and how they abstractually branch into universal knowledge, an ultimate goal for him.
Actually, truth be told you may find it very interesting to read Descartes Search for Reason
. It may lend some insight into your preliminary ideas to check any deceivers in your own life. Believing in yourself may be reflected in the parts where Descartes discusses logic, emphasis on intuition, geometric certainties, etc. On your second idea, perhaps the concept of clear and distinct ideas (common throughout most of Descartes work) would be of increased interest to you. And maybe, as to your third idea, perhaps you may come to some very interesting parallels with Descartes abhorrence of patterns but rationalized knowledge. Good stuff Platorepublic!