1) Know who your characters are:
A problem I have when writing is delving into a story with half-formed characters. It saves a lot of time and hassle if you plan your characters out fully before beginning to write; otherwise, you'll have to make them up as you go along, which never works too well.
2) Find your setting:
Another important detail is where your story is going to be taking place. It's okay if your setting changes throughout the story -it should- but it would be wise to lay out your first setting very carefully. Where a character lives can speak volumes about their personality so the setting is very important. Also, make sure to develop the setting with vivid details so a reader can picture it more clearly in their mind.
3) Outline everything:
I personally despise planning out every detail, but it can really help when trying to develop a plot. You can always change or add things but when you first begin writing, it can really save a lot of time later. You can also leave some things up in the air if you're not sure which way you want your story to go, but be sure that you have a clear picture of the story from the exposition to the climax to the resolution.
