I might not be a good person to answer this because I am very much the sort of person that has a hard time staying on a character. A lot of the advice here looks good and some seems to include being less complete in your character write-up, and I certainly hope that helps you, but I don't even have that problem.
From my own experience over the years, I've only had a handful of characters that I can think of that I had any real success keeping for any length of time, and the common thread for all of them was making the right connections early on. What is the "right" connection? For me, it was the availability of a handful of people that I enjoyed playing with who were present when I was. That was it, basically. Every concept I have, every character I CG and get approved, has excited me for some amount of time, but it was never the concept that nailed it so much as the people I fell in with. Also, it couldn't just be one good interaction, or unrelated scene. Chance or circumstance had to get something rolling with those folks beyond the standard coffee-shop name-swap. I just don't have the perseverance otherwise, which is a personal flaw that gets me rather easily, and accurately, hung with the a sign that reads: Flake.
tl;dr Focus on finding the right people at the right time (really important) and worry less about any weakness in your CG process.