Main clause: There are many areas Subordinate clause modifying “areas”: (that) you can focus on to improve your creativity. Note that “that” is optional in object restrictive relative clauses. Note that it’s also acceptable to introduce this subordinate clause with which, in which case we could (in formal style) move “in” in front of “which”: on which you can focus to improve your creativity. Personally, I prefer the original, with no introductory object pronoun.