Length! Oh dear god. (For more on god, see my novella, The Funeral.) 

I used to think that in order to be a real writer, you need to write full length novels. And that, my friends, is an amateur talking. 

In my experience, you can’t force your story to be any longer or shorter than it needs to be. In order for it to be the best it can be, you will need to let it be exactly the length that it is. Stephen King has a rule to make everything he writes 10 % shorter in the second draft, and while I have nothing against cutting unimportant words and chapters, please do not try to cut the 10 % by force. 

Same goes for the opposite: do not add unnecessary words, chapters, or events to your story just to make it longer. Unless a word or a series of words moves the story forward or provides information about your characters, your best bet is likely to leave it out. 

Unless, of course, the point of your work is exhaustive description, in which case go ahead.