Just keep doing it, honestly. There seems to be a big real fear from people at giving it a go. People want things(tm) to do, and games will stagnate and die without it, or atleast to me they will be unintresting. You don't need to be the gift from god, if people are having fun you are probably doing something right.
Obligatory, have atleast a not utterly terrible grasp of the rules regarding atleast the themes you wish to make use of.
I honestly (and sometimes to my woe) just think up stuff I'd think be cool to happend to my PC and then I run that for whoever is around and wants in on it. This is also because atleast I know it is stuff I enjoy, in the way of themes and you do need to be able to enjoy yourself.
Keep things going, try and avoid getting bogged down in big OOC discussions or the like. Keeping shit streamlined helps immensly, for myself atleast. Also for me that means that pose order goes right out the window if we're not in combat, 3 pose rule at most. If someone is taking way too long, skip em.
Have an idea, hell write down planned scenes, but be prepared to change shit. Improvising is a talent you get better at with time.
Some scenes will suck, be frustrating and utterly not enjoyable. And it might not be on you (wholly atleast) sometimes things just go poorly or you get people who can't interact with you/the world/whatever much.
There is something between one-shots and utterly complicated metaplot level crap, people appreciate a sense of continunity and as is the common trope but, if something/someone sticks around for several encounters they will get a relation with it and it will be sweeter once they resolve whatever it was.