Try Power Priming

To display confidence and be perceived as upbeat and positive, think of a past success that fills you with pride and confidence. (This doesnt have to be taken from your professional life although I do encourage clients to keep a success log so that they can easily find an event.) Then recall the feeling of power and certainty and remember or imagine how you looked and sounded. Recalling that genuine emotion will help you embody it as you enter the meeting room or walk up to the podium.