I know there are a lot of myths out there, half truths, and out right lies about this, but I am going to write a few things that I have heard.
Anything that promotes health and physical fitness increases sexual performance. Any kind of exercises that increases the blood flow is important here. I have read that if you do the squats you will exercise the groin area and increase the blood flow. Also greater physcial strength and endurance helps. I think walking helps. Walking does a lot of good things for you physically.
The other thing is that some perscription drugs impedes sexual performance. It you have to take them, you have to take them, but reading the possible side effects is a good idea.
Also having a loving relationship with your spouse is good also. It works better if your not having a fight, unless of course you kiss and make up first. Also only having sex with your spouse is the only way to go. They have actually learned that having sex with other people that you shouldn't be having sex with adds to the stress and takes away from the enjoyment.
Stress also works against sexual performance, so get rid of the stress first. Being worried about something doesn't help. Keeping a good attitude and being happy goes a long ways here. Singing and making a melody in your heart to the Lord will help in all areas of life, like keeping a merry heart.