Writing a first novel is a very exciting experience.
In many ways it’s the easiest novel you’ll ever write. There’s no deadline for example. You can take as long as you want to write it. There are no expectations from anybody. With a second novel (assuming your first got published) everybody - you, your family and friends, your readers, your agent and your publisher - will be wondering if it was as good as your first.
If your first novel didn’t get published then writing the second can be harder, as your confidence can be somewhat knocked. (Use EFT to regain your confidence and solve this problem.)
When writing a first novel you can play around with ideas, and genres, and you can experiment to your heart’s content. There’s an innocence about it; the sense of a child playing, engrossed.
You can indulge yourself in learning so much about writing, using resources like this website and others.
Of course, for sure you want this novel to be published, but you’re enjoying the process for its own sake.
(Or you should be. If you’re not, question why you’re doing this. Is it that you want to get rich writing fiction? If you’re not enjoying the process, then I strongly urge you to give up now and to go and find something else more satisfying for you.)
So, if all is as it should be, you’re loving the whole process for its own sake.
Having said all that, there are ways in which writing a first novel is harder than subsequent novels.
For a start you have to find the time to do it in an already busy life, and that's not easy. Do remember that everyone writes their first book (and many subsequent books) as well as the day job, so it is doable for sure.
And then, as you're writing, you’ve absolutely no idea if it’s any good or not. You’re working on your own, possibly without feedback. You’re putting hours and hours of your life into this project with no clue if it’ll succeed. (Which is why I recommend defining success differently.)
However, if your first novel was published then you can bring an increased confidence to your second. You know you’re publishable. You probably have at least a two-book contract, so you even know that this novel is guaranteed to be published. It’s a great feeling!
You don't have that feeling with your when writing a first novel. So I strongly urge you to just enjoy the process for its own sake. For sure, write the best book you can; I'm not talking about half-assing it. But just take the pressure off yourself.