The 29-year-old struggled to make an impression in the first team and was happy when the former Liverpool boss left at the end of last season.
"It was frustrating and I never want it to happen again. That's why I'm so hungry to do well now," he said.
"It was very difficult but I was lucky to have coach Kevin MacDonald with me when I was training with the reserves.
"He kept me on top of my game and made sure my head was right."
Warnock has been a regular for Villa this term, starting all seven of their Premier League matches so far.