Character development is perhaps tedious but worth the reward when they step outside your mind to grace the pages authors fill. If the author does not care enough about the character, the reader will pick that up.
Several tips help in different ways that authors stick to. For example one may have a character sketch.
These drawings may intimidate you, but please find one and print it out and list what your character is in height, age, likes, traits, and so forth.
For me I have a character sketch for each character from the major ones down to the minor ones.
I know their heights, their abilities, their age, whether they have magic or ordinary average Joe or Jane. What kind of hair and eyes do they have? How do they view others?
It seems very complex but aren't we all? One other way I recommend is a character bio summary. Write out in two or three paragraphs what they are like, what they endured so far or why they are what they are and what they do.
Make your characters stand out from the rest!
Of course if your character is supernatural or has powers, make out your own list how you wish. Remember it's just you and the page and the image in your mind to bring them to life on paper.
What technique do you have that works helping your characters build character?