Make a Background Story for All Main Characters
Family, childhood, interests etc.
DETAILED ALOT!!!!!
Get to Know the Characters (For you and the reader.)
2. Make the Character Flawed
Not all Characters, but main, main ones.
Flaws that Agree with the Backstory
3. Know How the Character Speaks
Age Appropriate
Stay the Same through the Entire Book/Story
4. Trust Your Intuition
If It Doesn't Seem Right or fitting in, Save it for Later, or simply don't write it.
5. Every Action, Has to Have a Reaction
If someone dies, the reaction should be sad, or upset.
If someone is proposed to, the reaction should be overly excited, happy, even a few tears of happiness.