It is important to let yourself write and then let yourself edit and treat the two as two separate tasks. You don’t want your editing side to get in the way of your creative side. And the things you cut might work their way into future stories if good enough. Stick to the point of your story, always.
When I'm ready to do so, I edit, and edit, and edit. First edit is to get rid of repetition, including all unnecessary adjectives. Second edit is to look at the plot as a whole. Does it work? Is anything missing? By the time I get to a third read through and edit, I can usually spot where I can tighten the novel and/or short story up further. At that point I think about sending it off somewhere!
Do spend time reading your work through on paper. I’ve lost count of the number of things I spotted on paper I totally missed on screen. There must be a psychological reason behind that but it won’t impress an editor! I always use the reverse side of anything I’ve worked on as scrap paper.
Ensure toner/ink cartridges are up to scratch. If you’re wondering whether you need to change them before sending anything out, the answer is yes, you do! Editors/agents are looking for reasons to turn you down so don’t give them any!
Get your story down on paper first before you even think about editing. Some authors do edit as they go but the disadvantage to that is it can take a lot longer (will you ever find the perfect sentence?) but if you get your story down, you know you have something to work with.
Do put your story or novel aside for a while after writing. It’s normal to think you’ve written total rubbish just after finishing your tale! Give it some time and you can read it with a “clear” mind and sort out what really is rubbish and what isn’t. I can never judge my work objectively directly after writing it. That applies to this too!