Actually, the easiest way out of this is better writing: "The DM first describes the room, then indicates what monsters are present." Or "The DM describes the room, and then describes the monsters in that room." No need for the pronoun at all, and I suppose you could throw 'to the players' in there somewhere, but isn't it assumed by the reader, in the context of (say) a module, that the DM is addressing the players?
That works well for a single, isolated sentence, but in the context of a paragraph or chapter, it leads to highly repetitive structure that becomes less easy to read. "The DM does X. The DM does Y. In Z, the DM then...." The whole point of pronouns is to avoid the repetitive use of the specific reference.