Forrester admitted Villa captain Stiliyan Petrov told him to jump at the move.
Forrester said: "I spoke with Stiliyan before I moved. He was a legend at Celtic and warned me the SPL is physical and to get on the weights!
"He pulled me aside in training and asked if I was going to Killie. I said 'yes' and he told me to keep my head down, work hard and it would be good for me.
"Stiliyan was very encouraging about the SPL, he enjoyed playing up here and he felt he came on a lot as a player.
"I want to improve by being here, get a few goals and push the team up the league.
"I also spoke to Villa's caretaker manager Kevin MacDonald. He also said it would be a good move and Killie would be a good club for me to join. I played with Ben Gordon at England youth level and asked him what it was like before I came and he said all the lads were top-notch.
"I was thinking of a loan before Martin O'Neill left but then when he went Killie started talking to Villa, so I didn't have much time to think whether I'd stay or go."