Zinc prevents the conversion of testosterone into estrogen. It also aids both sperm count and health. However, zinc will probably only have a noticeable effect on your testosterone levels if you are currently deficient in it, though I feel that it is still worth mentioning.
Lose body fat
Body fat, also know as adipose tissue, is a large storage container for aromatase. Aromatase is an enzyme that converts androgens (hormones largely involved in male characteristics, such as testosterone) into estrogen. Therefore, losing body fat increases testosterone levels while reducing estrogen levels. However, trying to lose excess body fat by extreme dieting is also detrimental to testosterone levels. The trick is to lose weight slowly, this is why many personal trainers will tell you to only lose a few pounds per week at most, as this is healthier for your body.
Plastics contain synthetic estrogens called xenoestrogens which again lower your testosterone while increasing your estrogen levels. For this reason it is better to drink from stainless steel bottles if you can.
Short durations of high intensity exercise have been shown to increase testosterone levels. However, aerobic exercise for moderate to long durations have been shown to have either no effect or to have a detrimental effect on testosterone. Apparently the best exercises for raising testosterone are compound exercises of which you can only perform 5 repetitions for 5 sets.
When we are stressed our bodies release cortisol which is a hormone that inhibits the actions of testosterone. This is a particularly common problem in modern culture as our lives are very stressful, also, having constant worries has a strong impact on both our ability to fall asleep and our sleep quality, both of which have a dramatic effect on our testosterone levels. Sleeping for around 8 hours per day is recommended in order to reduce our cortisol levels and keep our testosterone high. Practising deep breathing exercises is also beneficial for reducing cortisol.
Cut down on sugar and alcohol
The consumption of both of these can lead to large reductions in testosterone. They are both large problems in most peoples' lives as sugar is in many foods and a lot of people drink alcohol. Some studies indicate that drinking heavily can keep testosterone levels low for a few days if not a week. This is particularly detrimental to those of us who drink heavily each weekend.