You are separating dialectical and materialism as if they are separate methods, and while there is a difference between what each word means, they are not mutually exclusive the way you seem to be describing them, and it is simply an incorrect view of what "materialist" means. Remember, Marxist philosophy is Dialectical Materialism. Dialectical thinking is almost entirely about recognizing the contradictions within a thing that drive its change. Materialism on the other hand, is not "thinking only in terms of immediate causes." Materialism is merely analyzing any thing or issue or system by putting material reality forward as the primary causal force rather than driven by human ideas or by spirits or by some magical secondary universe (like in Cartesian Dualism). Where you said "see a system as it exists due to historical conditions and present conditions" - that is materialism, while the dialectical part is again, identifying the contradictions within a thing as what is driving that thing towards change.

To more directly answer the OP question, an easy way to approach a dialectical kind of thinking is to consider the old school platonic meaning of "a dialectic," where, when trying to understand an issue, you approach it with a given perspective but then consider what someone with an opposing perspective would say as an argument against your initial perspective. That is a very simplified way of beginning the process of thinking dialectically.