This may be included in (4), but I think it merits elaboration:
Build your character with motivations, personality, and mannerisms. (Roughly in that order of importance.) At least for me, having a strong idea of what my character WANTS is the biggest part of having fun with the character. Whether it be minor goals that you can achieve in each session, or an overarching goal you may only reach in the epilogue, I find achieving these character goals to be the most rewarding part of plays.
Personality and mannerisms are what make your character distinct and memorable. (I really enjoy when people have a voice in-character, both because it makes the character come alive, and it really distinguishes out-of-character chatter from in-character dialogue.)