yeah. dont send it off before you are done. I've heard so many people say "well, by the time I get a response, I will be done." the agent or editor could ask for a full manuscript the day after you send it. it's happened. then you will have blown your chance. in addition, you don't know that you can finish a novel until you have actually finished it.
You send your manuscript to an agent first--though some cases it is ok to send to an editor first, it just makes it hard to get any sort of bargaining power on the contract that way. If you don't personally know an agent or an editor, you send query letters, and then the manuscript when/if they ask for it.
If you feel comfortable that your manuscript is good enough, send it out. It doesn't have to be perfect (thought the first 3 chapters/30 pages should be as close to perfect as possible). I've read manuscript submissions that were given to Brandon's agent Joshua, and they were rough. If there is a glimmer of writing there, and a fantastic idea and story, you have a shot. If you feel like you are just tinkering, stop wasting your time and send your query/manuscript out while you work on your next project.