Here are two ways to do this:
1) In iTunes, go to Edit > Preferences > Devices. One of the lines you'll see is something like "prevent iDevices from syncing automatically." Ensure that box is checked.
2) with your iPad connected, go to the Apps tab on the right side. At the bottom of the list of apps, next to the representation of your iPad's screen, is a box titled something like "sync new apps automatically." Make sure THAT box is unchecked.
That should stop your iPad from syncing automatically. Now, you're in charge.
Good luck and I hope this helps.
Marilyn