Well, first thing first. I would recommend you do a very conscious exercise and meditate about the fact that it will be a long journey full of obstacles and victories. This is intended to prepare your mind for those difficult moments that you will face somewhere in your adventure of writing.
I know I should be giving a bit of more optimistic advice, however, one of the problems writers face is the very famous, though also tenebrous “Writer’s Block”. When writers, especially new writers, start their stories, they do it from the heart and the emotion, and that is fine for it keeps the story’s heart beating, but they forget sometimes they are sentient beings and when they face those times, they feel it is a dead-end. Whenever you come to face this moment, embrace it! see it as an opportunity to check what you have been doing, and what could be done better. It is a moment for breathing new air and give yourself the opportunity to think that we are not perfect. Stuck does not mean dead, stuck means thinking out of the box and looking for new opportunities.
Do not let anyone’s opinion stop you from pursuing your dream of finishing your novel. See, there will be moments when you will need people to read your production, ask them to be truly honest and if the comments are not very positive, do not see them as drawbacks, but rather as opportunities to do it better. We can always do things better.
Treat your novel and its creation process as an adventure. Think of yourself as an adventurer who is about to go to the open and vast world in the pursuit of growth. Be open-minded to possibilities. The goal at the end can be publishing it, or making a hoard of money with it, but remember that the most important thing is all the process of making it, the lessons learned, the flaws identified, and the strategies applied to overcome them. Writing is a creative process, not of a book, but rather of the self.
BE CONSISTENT AND DO NOT HESITATE. I will never get tired of saying this. Let your hand run smooth and free on the paper. Do it every day, make a space in your daily agenda for writing sessions, and try not to miss them. Make writing a fundamental part of your routine. Sometimes, new writers start writing daily, and then they write 3 times a week, later 2, and then it becomes something that could have been but never was. So write, just write and write, the more you do it, the easier it will stick as part of your days.
Read. I know writing can be an exciting adventure and it may become the only thing we may want to do. However, reading teaches a better writer. Reading while writing will open your mind to styles, expressions, forms, and structures that could enrich your story.
START NOW! DO NOT THINK TWICE ABOUT IT. Do not delay it. Get that paper now, and start. The more you think about whether doing or not, the more you are exposed to let the creative itch go away.
Hope it helps! :)