You can do this exercise any time, anywhere. I do it while travelling in a bus or train, but not while I am driving.
The thinking behind this is that you can move from sexual energy to psychic energy and spiritual energy.
Focus your mind's attention on the tip of your penis (women could focus on the clitoris or vagina) and say in your mind, 'Fill me with your creative power' or 'Fill me with your life-giving power'. Don't think of the words. Don't think of anything. Try to focus your attention fully on sensation on the tip of your penis. If you get distracted, focus your attention again. It you feel any pleasure, allow yourself to enjoy the pleasure and relish it. Get rid of any inhibition. If you don't get any pleasure, don't worry about it. If you get an erection, let it happen; accept it and be happy about it. but if there is no erection, don't worry. Don't compare today's experience with yesterday's. Totally avoid performance anxiety. What happens today is good for today. Practice regularly for 15 minutes every day.
At first you may not feel any sensation there. After some days of practice you will feel the sensation. After some time you will feel the pleasure more and more . After a few months the mere invocation of the words will make your genitals come alive. Keep up the practice for a few more months and you will see that you are becoming more and more energised and rejuvenated. In the advanced stage you can feel a spiritual energy entering through the genitals and permeating your whole being.
This has worked for me. I am sure it will work for you. The women could try this focussing on the attention on the clitoris or vagina.
I shall be happy to have your experience.