Get a copy of the latest Writers Handbook and read it first. An agent is certainly a good plan but if, for example, you want to write for Mills and Boon (no that is not an insult, they pay bloody well) they will not entertain anything submitted by an agent. They will, however send you a set of criterea by which they decide who to publish and who not. It depends what you are writing and where you see your market. I have a feeling we have had this conversation elsewhere (pos PM) some time ago. The Writers Handbook tells all.
I write, I publish, I edit. SWWLTBO teaches "Creative Writing" ~ Any help we can give is yours.