First, you just need to figure out your novel’s outline:

Main character (who leads the story)

Status Quo (situation at the start)

Motivation (what your character wants)

Initiating incident (what disturbs the status quo)

Developments (what happens next)

Crisis (how things come to a head)

Resolution (how things resolve)

Your book should be a little bit like a roller coaster, with a few small ups and downs, and then a big one (climax). Many writers use the three-act structure:

Act I – Setup: Exposition, Inciting Incident, Plot Point One (about 1/3 of the book, or about 1/4 = 100 pages).

Act II – Confrontation: Rising Action, Midpoint, Plot Point Two (about 1/3 of the book, or about 2/4 = 200 pages).

Act III – Resolution: Pre-Climax, Climax, Denouement (about 1/3 of the book, or about 1/4 = 100 pages). Fulfill any promises made to the reader.

Within each Act are a number of different “beats” — a plot event. The beat is the smallest unit of the story. It is the space between an action and the reaction it causes within a scene. A scene may be broken down into beats ­– marked only by the moments when the mood or relationship the scene describes changes. Two characters are having a conversation, character A says something which makes character B react in a different way from what A expected – that’s a beat.

Just start!
Don’t worry about spelling and sentence structure… just let go and let the story out, watch it unfold as your characters come to life (you will catch all the mistakes in the re-writes).
I have to tell you that the very first novel I wrote I had to read the start of many famous novels to get an idea of how to start a great novel… I start by writing the first third of the novel and then went and wrote the ending, coming back to fill in the middle chapters, only to find out I was 30,000 words short… and then I re-wrote and re-wrote until I loved the story.

Sometimes the plot comes after writing the book, there is no hard rule saying you have to know it to begin writing a story. BUT… you will need one.

Different plots

Adventure

Ascension – Descension

Discovery

Escape

Forbidden Love

Love

Maturation

Metamorphosis

Pursuit

Quest

Rescue

Revenge

Riddle

Rivalry

Sacrifice

Temptation

Under dog

Wretched Excess