[JeffL0]

Opt out of ATT settings which monitor your activity:

Go to https://att.com and log in with your account.

Click "Profile" in the upper-right of the second ribbon.

Click "Privacy Choices" on the right of the new, third ribbon.

Change all options to "off." (on mobile, swipe/scroll the screen right to see all options that can be disabled)
Save your changes.

These settings are enabled by default and enable AT&T to know more about you than you'd probably like.

[JeffL0]

Regardless of who your provider is, a further step you can take to not disclose your DNS queries to your ISP is to change your DNS servers. You can do this at a machine by machine basis, or at the router level (if using a router other than the default ATT modem, they lock the DNS settings, so you would have to override the requests locally for each device).

8.8.8.8 for example, uses Google's DNS rather than ATT's. There are many others, e.g. 1.1.1.1 (https://en.wikipedia.org/wiki/1.1.1.1) or 9.9.9.9 (https://en.wikipedia.org/wiki/Quad9)