Read outside the genre. It will help the scope of new and original work. When writing something set in a quasi-medieval fantasy world, read some history of the Dark Ages or the Middle Ages. When writing about alien contact, read some history on New World explorers and read some hard science for propulsion engines, rockets, and planets. When submitting, first request the submission guidelines from both agents and publishers.
Many agents have a knack for editing.
Some are better than others. Some don't edit at all. If you want an agent who will help you develop your writing, ask. If you don't want an editorially minded agent, ask. The agent will work for you but will also help you in your professional career.