Using the breath as an anchor is a classic example. However, the breath can be too subtle a sensation for many of us.
One tactic I’ve tried is to set a repeating, silent vibrate alarm on a Fitbit device, which has not been especially successful.
Another tactic I’ve heard of (but haven’t tried) is to wear a non-medicated “intra-nasal” menthol inhaler. The idea is that this makes the sensation of the breath much more noticeable, although I’ll admit it seems a bit extreme.
What method have you had success with?