Heavy metal, fluoride, chlorine, pesticides, dioxins and other dangerous chemicals that are in our food, products and even the air we breath are wreaking absolute havoc on our endocrine systems (responsible for testosterone production). It’s hard to avoid these (especially if you’re a smoker) but they are major contributors to man’s decline in testosterone.
^ Mehta PH, Jones AC, Josephs RA (Jun 2008). "The social endocrinology of dominance: basal testosterone predicts cortisol changes and behavior following victory and defeat" (PDF). Journal of Personality and Social Psychology. 94 (6): 1078–93. CiteSeerX doi:10.1037/0022-3514.94.6.1078. PMID 18505319. Archived from the original (PDF) on April 19, 2009.

So if you’re intent on maximizing your testosterone levels, and/or you have applied all of the above and you’re still not satisfied with your results (which would be surprising) then you could try the below. I will point out that some of these tips may not have the scientific evidence to back them up like the previous points, but I can assure you that either I have or do use them (and have positive results), or a client has used them with pleasing results, or finally it is such a new conception that there isn’t enough evidence to prove it one way or another.
Our culture sees meat and fat as the enemy, while carbs and sugars are treated like gold. High fructose corn syrup is in almost everything you buy, and this sugar is known to wreak absolute havoc on our endocrine systems. Food companies are well aware that this stuff is destroying you, but as long as people continue to indulge on it they will continue to produce it.

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Sharma, R., Oni, O. A., Gupta, K., Chen, G., Sharma, M., Dawn, B., … & Barua, R. S. (2015, August 6). Normalization of testosterone level is associated with reduced incidence of myocardial infarction. European Heart Journal, 36(40), 2706-2715. Retrieved from https://academic.oup.com/eurheartj/article/36/40/2706/2293361/Normalization-of-testosterone-level-is-associated