Mental training during tennis might be an overlooked area during a tennis lesson especially for recreational players. After all, we are just looking for some fun and exercise. Perhaps for the more serious recreational players who demand more from their shots could find it useful to train their mentality.
Many times we fight the negativity after a bad shot , especially more when it happens many times during your tennis session. The habit of detaching emotions from your poor performance and focusing on your next shot is harder than it looks. One way would be to focus on your racquet and arrange your strings to divert your attention. You might see that happen often on the professional tour on TV.
Furthermore, instead of wasting unnecessary energy venting your frustration, channel that energy to your next shot. I know, we are only human and not just in tennis but negativity applies everywhere in our lives. Find that strings on your racquet and start arranging them for a few seconds to reset your focus for the next shot.