There are two ways:
1) In iTunes, go to Edit - Preferences - Devices. Tick the box that says to stop automatic sync ing of iDevices
2) With th iPad plugged in and connected to iTunes, on the Apps tab, underneath the list of apps, there's a box to auto sync apps. UNtick that box.
With those two things done, you are in charge of what iTunes does when your iPad is connected - it will not do anything automatically.
Hope this helps.
Marilyn