Rangers will take on Wigan in the first leg on Friday while Derby face Brighton in the other semi-final.
"Wigan will be a tough game - they're a very good side," said Redknapp.
"Being at home in the second leg is important for us, but our only focus at the minute is on preparing for Friday at their place.
"I think there are four very evenly-matched teams in the play-offs.
"Everyone will head into them confident of promotion, but we'll just have to wait and see what happens.
"This league is so unpredictable, and I don't see the play-offs being any different. It's all up for grabs for us - we're going to give it a right go."