As anyone in a Differential Equations class could tell you, there are a lot of different strategies for solving differential equations. I found it helpful to organize many of these strategies into a single document.
This document is intended primarily as a reference guide. It contains complete proofs of each of the techniques it discusses, and also covers the relevant definitions and properties relevant to the various types of differential equations. Topics covered include separable and exact equations, reduction of order, variation of parameters, judicious guessing (undetermined coefficients), the method of Frobenius, Laplace transforms, and higher-order equations.