Instead of writing out the dialog and the action and all those details, first come up with the setup:
Our protagonist wants his girlfriend back.
Somebody else (the antagonist) wants that to not happen (could be the new boyfriend, could be the father...)
... it could even be the girlfriend's boss
Protagonist comes up with a plan: go back in time.
... fortunately he is the head of the Time Machine Company
Put some difficulties in his way way:
... it costs a lot of money to go back in time, so he's going to have to come up with an excuse.
... the board approves the trip back in time (under these false pretenses) but our antagonist needs to come along too.
etc... until your basic plot line is complete. Don't actually write
the story yet. Now go back and ensure that the story actually flows well. If you are like me, you'll find that there are many things that need adjustment. For example, Fred needs to have known about Susan's betrayal before he can confront her. Or, he will need to have been (believably) unaware of it when he meets Susan (and would otherwise confront her). So, that tells you scenes that need to be put in between. You'll find other scenes that are not necessary... for example it may turn out to be unimportant that Fred was just
made the head of the Time Machine Company... in which case you can drop that (still unwritten) scene and replace it with a sentence or two that merely establishes his position.
Once all the structure (the story itself) is laid out, then you can start writing the action, the dialog, the description, and all the other stuff that is the actual writing
of the story.
Or, you may find that that particular story doesn't work at all. You can then drop it and move on to another one, with little wasted effort. In the future, parts of that (unused) story will probably make their way into other stories you dream up, and will work out better.
No matter what you write, there will be parts that work out better than other parts. That's ok. Only the mediocre are always at their best.