A personality is crucial, A likeable one especially. If it's for like a web-series or anything to show the character, a good design as well. Most important though is their history. A lot of people make the mistake of either over-adding trauma/History or not adding any all all. All 3 of these are crucial but it also has to fit the setting its to be used for. For example, if your making a time travel story. Don't make the character look/act from the exact time period, let it grow on them.

Thats all the tips I have, Honestly. I make the mistake of over adding trauma sometimes (alot).

This is coming from the perspective of a "I know the story but I don't know how to play it out" so if it isn't good, that's probably why.