The first step toward building a healthy bankroll is to become a winning player. Most players lose, including most players who think they are good players. If you are a losing player, you should set a budget, and have fun within that budget, but you can't expect to build a bankroll.
Online games are generally much tougher than live games for the same stakes. People don't go to a casino to fold, so they play a lot of losing hands, which makes it easy to win money, at least before the rake. If you beat the lowest stakes live games, with a $2 or $3 big blind, that may mean you can beat the lowest stakes online games, with a $0.02 big blind. It's generally very expensive to think of yourself as a NL $100 player because you beat live games at those stakes, and then insist on playing NL $100 online. Expect to have to move down a lot. The good news is that you get a lot more hands per hour online (particularly if you play multitple tables), the rake is lower, and learning to play without relying on physical reads will improve your fundamental skills a lot.
Second, and it is a very distant second, to avoid redepositing once you have a winning track record in some level online, you should exercise some form of rational bankroll management. See
this post.
As for books, ones from 2+2 are generally good. Make sure that you are getting books related to NL. Not long ago, there were very few NL ring games. Books didn't even have to mention that they were about limit hold'em instead of NL. If you get a book on limit, you will probably be disappointed, even if it is very good for limit and a few of the ideas carry over.