Many seek instruction and advice before attempting to write. My advice is to just write. In doing so you begin to learn what type of writer you are.
Some writers plan and outline, meticulously. However, the downside to this is that the writing becomes a chore. It's like sitting through a movie that you've seen before. You know what's going to happen. There are no surprises.
Some may advise that you put the work down for a while and return to is with fresh eyes. A break can work but you run the risk of totally losing the groove.
My method suits me, due to my style of writing. I'll call it 'the fattening'. I re-read what I've written, examining the characters in particular. You'll find attitudes and behaviour that may need justifying or explaining. You'll find opportunities and inspiration to launch sub-plots, which, in turn, change your thinking - ultimately impacting the story.
I was writing a story about two teen girls (17 & 19) whose father remarries, and immediately goes to work overseas for 18 months leaving the girls with their new stepmother. Obviously the girls view this new woman as the evil stepmother and a battle royal ensues. And, yes, eventually the stepmother wins them round. - a fairly predictable, standard sub-plot.
On re-reading I discovered I'd missed an obvious twist. The sub-plot start with two GIRLS missing their father and hating their stepmother. But without any propaganda or influence the sisters become angry with their father. They have become WOMEN and have adopted a woman's POV. "You don't marry a 36-year-old woman, a woman in her prime . . . and put her out to pasture - it's disrespectful and it's wrong!"
From this revelation new scenes and conflicts arise. (Particularly for the older sibling). As her father's daughter, the thought of other men hitting on her stepmother disgusts her. But as woman, if her man f**ked off for over a year - damn right she'd cheat on him!
I didn't see any of this coming until I'd read what I'd written, and looked a little deeper.
Hope this helps.