It depends which style guide you are following - but I couldn't find any that corresponded to "lowercase short words" (So "The Lord of the Rings" not "The lord of the Rings").
Grammarly suggests you capitalize the first word, all nouns, verbs, adjectives, and (implicitly) pronouns and adverbs and then says different style guides differ on how to handle articles, conjunctions, and prepositions. Some call for them to always be lowercase, and some for them to be upper cased if more than five letters.
Daily Writing Tips adds the last word and "subordinating conjunctions" ("as", "because", "although") to the "always capitalize" list (and discusses more the various style guides).
Everybody seems to agree though that "The This in a Title" is correctly title-cased.