You sound as thought you may not have been there before so some advice.
The car parks are HUGE, so make a note of where you are so you can find the car at the end of the day.
Take your lunch with you, dont leave it in the car to come back and pick it up later, you wont feel like the long trip back to the car just for lunch.
There is a monorail that takes you from the car park to the main park, and back again at the end. There can be big queues for the monorail but you can walk to the main park in about ten minutes, just follow the crowds.
There can be HUGE queues to buy tickets when you get there (I had to queue for about 30 minutes to buy a ticket last year before I could get in). Consider buying your tickets in advance and just picking them up on the day.
Once inside the park it is huge. The different "lands" are quite a way from each others and you can spend most of the day walking from one "land" to another.
Look at the map, and plan your day carefully so you dont spend all day walking around.
In the past I have visited Alton Towers and felt I have spent the whole day either walking around, or in queues, and about 15 minutes on rides.
Try to stay till the end of the day. Many people leave before the end of the day and the queues become so short you can just walk straight on some rides.
Also note that Alton Towers is in the middle of nowhere (worst place to build a theme park really) so follow the signs and be prepared for some narrow winding roads as you get near the park.
And dont leave valuables on display in your car, lock them in the boot. Some people do go round looking to break into cars.
Have a great day.