Like any sport, profession, hobby, pastime, or pretty much anything in the universe: Practice makes perfect, or as close to it as you can get. How much practice? Think of your ability to write as if it were a muscle. The more you work it, the stronger it is. Don't wait around for your muse to get their head out of the clouds. Write every day, at least a little bit, and it will become easier and easier to get the words flowing. It doesn't have to be on your current work in progress. It can be completely random, just get those juices moving!
If you have ever submitted to an agent or editor, you know exactly what I mean. And no, hitting refresh on your email a thousand times in one hour isn't an exercise in patience. Finish your book. Have patience while you let it sit and perculate. Come back to it in a week, a month maybe, then revise it. Have patience when you are researching agents and editors. It can be tempting to send out those queries right away. Resist! You need to pick those you are going to sub to carefully. This takes patience. Once you find them and submit to them, again you must exercise that patience and wait at least thirty days for them to respond. Check their website to see how long they typically take to respond, don't bug them until that date. If they don't list a timeframe, thirty days is safe to assume.
No luck placing your first novel with an agent or editor? Welcome to the norm. It is tough to place your first book because you are going to grow and improve with each novel you write. Which means; while that first book is one submission, you should be writing the next one! Don't place all your eggs in one basket. Write th
e next, and the next, and the next. Want your book to be a series? Get that second one going! Not getting any bites? Keep improving your writing skills. Go to workshops, retreats, conferences if you can. If you can't, get books on the craft of writing that are relevant to your genre(s).