There are as many philosophies about what to do when you've finished your first draft as there are writers (probably even more, as I'm sure some people could claim more than one). Here's what I've done so far, and how it's worked out for me.
When I finished the first draft of my first novel, I celebrated - I think I had a nice dinner or something. I'd never written a novel before, and it was a great feeling. It had taken me more than six months, writing fifteen minutes at a time. After the dust settled from all of the celebrating, and I let it sit for a while, I went back and read through parts - and realized that I really didn't like it very much. Life intervened.
When I finished the first draft of my second novel, I was thrilled. I'd written it during Nanowrimo (meaning that I wrote 50,000 words in one month) which I considered quite an achievement. Right away I printed off a hard copy, which I hadn't done with the first novel. That made it feel more real, and I even committed to reading the whole thing through from start to finish. It wasn't a bad story. In the meantime, I started writing the sequel to the novel. And at some point realized that the real story started halfway through my first novel, and needed to be changed radically, and so I gave that one a break as well.
The third complete novel took me a little over a month. The idea for it appeared out of nowhere, and I didn't spend a lot of time plotting how it would look. Instead, I just jumped right in and wrote the whole thing. I was glad when I finally put "END" on the bottom of the manuscript, and again I printed it out to have the physical thing in my hand, to make it a reality that I'd actually produced something that was, if not publishable, at least an admirably thick stack of paper. This time, however, I went a step further, and started giving out copies to friends and families. I'm feeling pretty good about this one, and now that I've got people reading the story, it means I have to take it as far as it will go!
So far, the best comment has been this: "You could totally get this published. There are books out there that are way worse than this. Wait, no, that sounds bad! I mean your's is better than some I've read, that have been published!"
In summary: finish your first draft. Print it off so you have something to show for it. Get people to read it. And then read it yourself!