Something I want to learn...

A though just recently entered my mind about Agnostos (the 3-part thing I'm writing) and I've been thinking on it a lot lately. I have a guy who is going to die in it... and I was going to kill him within the next couple of chapters. But now I'm not sure that I want to kill him yet... You see, I realized that I hadn't really developed him in the readers mind as someone they really like and wouldn't want to see die... so they would have no feeling about him dying. So overall I'm thinking that I will just keep him for a little, and maybe develop him a little more. Yet, I'm not sure that there's a whole lot I can do to fix my mistake without going back to the beginning, and altering some things.
Does anyone have any suggestions on how I can develop my characters better from the beginning?

To start off...

Hello! To start off... I will tell you a little about my writing life...
I am currently writing either a trilogy or a single book split into 3 sections in it (I can't decide)... and I have a little over 60 pages, and 20,000 words. I must say that what I've written so far could be a lot worse, but I know that it could be a ton better too.
I also just recently started writing a book with my bestie, and I must say it has been quite fun so far writing with another person, and including her style with mine (we're really quite different writers).
I'm still working on my techniques and stuff and am really quite new to the world of writing... so if you're a writer, or maybe have some tips, please feel free to share!