oo mhh i think a good way to start is: what do YOU want to read that you haven't read before, or what you haven't read enough of?

if you're immediately thinking: god there needs to be more handholding. let these two characters hold hands. why isn't there any HANDHOLDING. one of the most impotant things while writing imo is motivation. if you're not writing the most self-indulgent piece of fiction that is catered to you first and foremost, you'll have a hard time sticking through with it.

if you're concerned about whether you're good enough or if your grammar or writing itself is ok, then read other fics haha. read a ton, and take note of what they're doing and try following the same steps while doing it in your own way.

if you're talking about an OC story and liking writing your own novel, i unfortunately have no idea bc i just write fan content :') hope this could help you out a bit!! if you have more question, you're welcome to shoot me more or DM me on twitter^^!