You can take bus 306 at the east square of Xian Railway Station to the Terracotta Warriors and Horses directly . From the hotel, Xian Bus 14(CNY1/adult and one hour) or a taxi (CNY25 and 25 minutes)can take you from the hotel to the railway station directly.

One day is a little urgent to visit these three places by yourselves. But if you have a tight time limit, you can catch up time to visit Xian City Wall after back from the Terracotta Warriors in the afternoon around 14:00. Then walk to visit the Bell Tower before 17:00.
Ps: If it is your first time come to Xian, suggested that you take part in a one-day Xian Tour by which the guide will arrange van, dinner and visiting schedule well.