The best and most memorable characters are unique. Here are a few things to consider when trying to make a character stand out.
Every character should have something that he/she is excels at, something that only he/she can do, and something he/she sucks at. This also helps determine his actions in certain situation.
Have a character with quirks. It can be anything like something he/she does when having a certain feeling or in a certain situation. Or how he/she behave when in front of a certain someone. Have surprising quirks to keep your reader interested and learning new things about the characters. This can also add conflicts to his/her lifestyle or job. I think it's really fun to see character with weird and unique quirks.
Sometime, when you want to go the extra mile, consider these three in making a unique character.
Exaggerate your character to the extreme by making him/her the most or best at something. Here are 2 example of my characters.
Now surprise the audience, something that contradict their exaggeration.
Lastly, add sympathy to make sense of it all.