I, myself, have been trying to get more familiar with geometrical proofs. I'm not entirely sure, but perhaps reading some of Euclid's Elements is probably a good way to work with definitions, postulates, and common notions. A compass and straightedge is really helpful so at least the lines you draw are straight. These are just suggestions as I have known up to the basics of calculus but I am still in the process of formalizing thi knowledge.