The first one here is that no-one can proof-read or copy-edit their own work. You know where the story is going, you know what should come next and you know your characters. It needs someone who can give impartial, constructive advice and who can say, "Excuse me, but what happened in between you jumping off the cliff and appearing in Harrods in carpet slippers?" without causing offence.
Try to use life experiences - your imagination may be fantastic but for emotional pieces you can put in your own understanding and empathy and make your readers do the same.
Use a Thesaurus - keep one with you at all times whilst writing. Try not to use the same words repeatedly. I have just finished a book by a well-known author who used 'therefore' three times in the same sentence on more than one occasion.
The same author also used 'And' at the beginning of almost every sentence throughout the book. This is useful if you are writing media/advertising material and need to get a point across quickly in limited space but in a novel? As the late Terry Pratchett said, "Let grammar, punctuation and spelling into your life! Even the most energetic and wonderful mess has to be turned into sentences."
Here are a few more:
Tina Fey - "It's a great lesson about not being too precious about your writing. You have to try your hardest to be at the top of your game and improve every joke you can until the last possible second, and then you have to let it go. You can't be that kid standing at the top of the waterslide overthinking it .. You have to let people see what you wrote."
George Orwell had a few - Never use a metaphor, simile or other figure of speech that you are used to seeing in print; never use a long word where a short one will do; if it is possible to cut a word out then cut it out.
James Patterson - "I'm always pretending that I'm sitting across from somebody. I'm telling them a story, and I don't want them to get up until it's finished."
But most of all - enjoy your writing! Again, as Terry Pratchett said, "Writing is the most fun anyone can have by themselves!"