Once you've completed tip #1, the next thing to do with your manuscript is edit it. Some people like to dive straight in, whilst others prefer to put the novel aside for a few weeks so that they can come back to it with fresh eyes. Either way, it's an essential part of writing.
When I first completed a NaNoWriMo novel, my idea of what editing entailed was pretty narrow. I read through it pretty quickly, corrected any typos or grammatical errors, then sat back with a big grin on my face, mightily pleased with myself. What I know now is that was not really editing.
Of course, spelling and grammar are an important part of editing, but I don't often have many of those mistakes to fix - I'm not bragging, it's just one of my strengths. They are just the beginning, however. Editing involves looking at the whole story arc and deciding if the plot, pace and characterisation are all used to their best advantage. It involves looking at your prose and your dialogue, and deciding if your writing is as strong as it could be. To properly edit, you have to pick through your writing, turning over every sentence and deciding if you've expressed exactly what you want to express, or if there's a better way of doing it.
I took a self-editing course with the Writers' Workshop, which was really valuable. You don't have to take a course, as there are plenty of resources online to help you with editing, but it's really a worthwhile experience having feedback from professional editors and writers, as well as fellow amateurs. The most important thing is not to rush it - producing an excellent novel takes time and effort, as I have learned over the years. If you put in the necessary editing work, you will see results in time.