Their characters' actions and reactions
Being looked down on but having spine, rather than not doing anything and sulking
Being helpful and/or compassionate at times (not all the time unless its a secondary character or the person can seem unrealistic and fake). Also sticking up for people is a good method
Human actions -- when theyre talking describe what they do. Do they pace? Do they scratch their beard? Do they scowl?
Use verbs and not just adjectives -- standing out can be enough to make a memorable character (which is another step toward the reader caring). He stormed across the room is better than he walked quickly. Also give them other quirks, like a man who's big can be compared to a bear -- he lumbered across the room, he crushed her in a bear hug, ''Don't touch that!'' He growled.
Humour also works quite well -- funny situations and things they do/say, just dont make it look like the character is trying to be a stand-up comedian because this normally wont work in your favour (unless he/she is)
You need to make them relatable, take realistic actions, and every action needs a motivation. Welcome to the hard part of writing!
(Characterization is touggghhh, make sure you have a GOOD idea of your chars before you start, not that im doubting that you do)
--okay, lengthy, i am done
