It's hard to give advice without more detail:
What kind of plateau: weight loss? strength gain? hypertrophy?
And what have you been doing? What does your weekly workout routine look like?
In general, it takes some kind of 'mixing it up' to break a plateau: a change in the type of workouts you are doing. If you aren't already doing so, and your plateau is weight loss, try adding one cardio interval workout per week to your schedule.
If you already are doing that, try some LSD (long, slow, distance) work, starting with walking maybe 4 miles, then increasing the distance by 10% per week. LSD work is supposed to train the body to burn fat for fuel rather than carbohydrate (though both are used to some extent).