After first draft

I set aside the first draft and do something else- I either do short pieces, work on edits of previous novels or have another compelling idea...I usually do one pass all the way through my first draft for grammar, spelling huge holes if I am so inclined but it works better to let it sit for a couple weeks...it's really up to you...
THere is nothing wrong with going back to old ideas from other stories- I know many writers that expand a short story into a full length novel- "Foaling season" was expanded into "The God of Animals"...

Congrats, billyf! Isn't it a great feeling?

I waited, but only about 3 weeks. My breaks in amongst the edits are frequent, sometimes up to a week, but I try to plug away without diving into another big project. I just don't want to distance myself so much that I lose sight of my goal. That said, each writer has different habits, different ways of producing to their best ability. You just have to find what works best for you. Good luck!

Congrats!

Let it sit for a few weeks and work on something else. That something else doesn't even have to be writing, if you're inclined to take a break. You could research agents to query, consider setting up a website, or just read for pleasure and call it "research" for your next book.

Congrats
It'll be months until I will be in your position...

I recall that when I finished my first serial, I intended to take a break before writing the next. I couldn't do it. I missed it too much and dove right into it (in fact I had cheated and actually started the thing early!). I couldn't wait to start the third one, and once this is done, I know I won't be able to wait to start the fourth.

Often a break is a great thing though. It's good to have several projects in the works at the same time, preferably of different genres/styles or in different storylines. If a novel gets to be too much, you could go back to one of your shorter stories, since they require less commitment to finish. (A novel takes a lot of commitment and might get tiresome after a bit.) It's also good to let the first novel sit a while. Plus, while working on short stories maybe you'll come up with a fresh idea for a new novel?

Congratulations!

Now take a break and rest on your laurels for a bit.

You'll know when it's time to write the next one - it won't leave you alone.

If you're having problems moving on to a different novel, that might mean there is more of the first story untold. Do you want to keep writing a series about the same MC but perhaps a different location, time and/or action? Think it out. This might be the right time to keep writing. Keeping on with the second of a series might also help when you eventually go back to the first book to edit. It might clarify some factors in the first story.