STEP 6A. See if you can fix your low testosterone naturally by correcting one of the common causes of hypogonadism (clinically low testosterone):
Many men find out they have low testosterone and want to immediately jump on HRT (TRT or testosterone therapy), because they just want some relief. However, this is not always the smart way to go. Let me give you just one just real-life scenario that really does occur:
A man has lowish total testosterone of say 340 ng/dl. He finds out at the same time that he is hypothyroid. He then corrects the hypothyroidism and boosts his testosterone to 450 ng/dl. Most of his "low testosterone" symptoms actually go away and he decides to wait before going on HRT, because he is doing pretty well.
Here are 10 Practical Ways to Fix Low Testosterone Naturally to boost testosterone 25% or more and/or often eliminate low T symptoms. Remember that these could potentially be additive as well:
1. HRT (Hormone Replacement Therapy). (100-1000%) Could HRT be considered a "natural" solution? It depends on your definition of course. Personally, I would say that it is a natural solution when you use a) bioidentical testosterone (or an esterized testosterone) and b) you stay within normal ranges. For example, let's take the case of a man that goes on testosterone pellets: the testosterone in the pellets is bioidentical and it will raise this man's T to around 600 ng/dl on average, which is a often a nice level for a man in his 40's and possibly 30's.
What kind of an increase can you expect from testosterone therapy? With injections you can take a man to whatever level you want. He can go from an abysmal 150 ng/dl and be 1500 ng/dl a few days later: it just depends on how much is injected. (Generally speaking, a man should not go over 1200 ng/dl, which is considered the peak testosterone of a very healthy young male. And most men should be under this to avoid side effects - more on that later.)
2. Anticipation and Sex. (25-70%) The mere anticipation of sex can send your testosterone through the roof. One study of men that attended a sex club found that those who actually participated experienced up to a 70% increase.  Even more interesting is the fact that this huge boost in testosterone occurred for men of all ages. Now I'm not encouraging sex clubs to boost testosterone. But you get the point: if you can figure out some way to increase the excitement and anticipation, your testosterone is very like to climb and possibly in a huge way. In fact, still other studies have shown that even hanging around an attractive woman elevates a man's testosterone.
Another example of this is the Cialis study where testosterone levels climbed by 24%. The reason is very likely the fact that men had more anticipation of and actual engagement in sexual intercourse, a proven testosterone booster as I show in link on Sex and Testosterone.
3. Weight Loss. (60%) Sorry to put a "boring" one at the top of the list, but weight loss can potentially give a man the biggest gains in baseline testosterone levels. If you are significantly overweight, your body fat may be aromatizing so much testosterone into estradiol (the "bad" estrogen) that it is actually signaling to your hypothalamus to shut off testosterone production. This is actually a form of lifestyle-induced secondary hypogonadism. So, if you take the time to lose the weight, it can yield big gains. I have seen a couple of cases of this on the forum and one study clearly shows it as well: men who lost about 60 to 280 pounds had an average increase of 60% in their testosterone levels.  Usually lifestyle changes will not cure hypogonadism, but this could very well do it. I have other studies listed in my page on Testosterone and Weight Loss as well.
Also it should be pointed out that these men generally dropped their estradiol levels significantly, thus greatly improving their testosterone-to-estradiol ratios. Some gains in testosterone are made but not enough to really get into safe territory. However, there is one exception: massive weight loss. ] Another study looked at a more general cross section of obese men that lost a much more significant amount of weight (between 57 and 283 pounds) and found, as one might expect, even more significant changes in testosterone. Total T levels went from an average of 240 to 377 before and after weight loss, respectively. This is a whopping 58% increase on average and is impressive to say the least. Free testosterone increased almost as much: 41%. (Free estrogen also decreased significantly as well.) 
This is verified by a couple of the studies on Aromatase Inhibitors, which basically reduce estradiol levels directly. One example was a study of hypogonadal seniors who were given Arimidex and experienced a 62% increase in testosterone levels.  Again, getting estrogen under control can have a monumental impact on testosterone levels.
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4. Elevated Prolactin. (50-100%) If you have elevated prolactin, it can suppress both your testosterone and libido. This can be from a tumor or other factors: see my page on Testosterone and Prolactin for more information
5. Lab Testing. (30%) How can lab testing stimulate testosterone production? Well, it can't directly of course. However, you can get a nice testosterone boost if your doctor finds you are deficient in any of these three tests: a) Vitamin D, b) Prolactin and/or c) Thyroid Hormones. These are inexpensive tests and all three can lead to nice testosterone boosts, again if you are low, of around 30%. Correcting prolactin can lead to potentially even bigger gains.
NOTE: There is one way that supposedly can lead to a 100+% increase in testosterone: abstinence. That's right - one study showed monstrous increases in testosterone right at the 7th day for men who could hold out from ejaculating for that long. I outline why I don't think this is a good idea for most men in my link on Testosterone and Abstinence.
6. Sleep and Sleep Disorders. (30-35%) Sleep and sleep disorders can have a profound affect on your testosterone and there are several reasons for it. For one thing, rising prematurely early can raise cortisol levels, which could lead to a drop in testosterone levels. Sleep also leads to lower libido, worsened mood and anxiety and other things that will affect your relationships negatively and that means less Sexual Intercourse, a Proven Testosterone Raiser. How much can sleep affect testosterone levels? The upper limit is probably defined by sleep apnea, the disorder where the breathing passageway is blocked and the sleeper is woken up multiple times during the night consciously or unconsciously. Studies show that apnea drops testosterone by about 30-35% and fixing your apnea will raise it by about the same. So this probably gives us an upper limit on what sleep improvements can do for your testosterone, since apnea is such a severe condition. See my links on Apnea and Testosterone and Sleep and Testosterone for more information.
7. Herbs and Supplements. (30%) Many men immediately turn to supplements and herbs for stimulation of their testosterone levels. Can these help? Well, first of all, we have to realize that there are two types of testosterone supplements: 1) fairly well-tested and well-studied supplements and herbs such as Tribulis Terristris and D-Aspartic Acid and some of the synthetic, laboratory-based stuff that is out there. If you read the list of ingredients and have no idea what is in there and you can locate no or virtually no studies on the compounds, then it is in the latter category. These kind of supplements I do not consider because they are, of course, very risky and there is little data. Pharmaceuticals are dangerous enough after a few stages of clinical trials. Can you imagine the risks of something cooked up in a lab somewhere? I just don't think it is worth the risk
Now, going to D-Aspartic Acid, this has been shown to increase testosterone by about 30% on average in one study. (Unfortunately, it can raise estradiol disproportionately though.) Other herbs and supplements have been found to increase testosterone at levels a little below this, i.e. provide a boost in the 10-25% range and I cover those in my Testosterone Herbs links.
8. Varicocele Repair. (~30%) A couple of studies show that in some cases - not all varicoceles are created equal - a man can get a nice boost in testosterone from the procedure that does the repair of this condition. For more details, see my page on Testosterone and Varicoceles.
9. Competition and Winning. (20-30%) Research shows that competition can raise testosterone levels surprisingly significantly. For example, one study found that men who watched a winning World Cup soccer team raised their salivary testosterone levels by almost 30%. 
10. Vitamin D. (25%) Can you believe that simply correcting a Vitamin D deficiency could boost your testosterone by 25%? Well, that is what one study showed. See my link on Testosterone and Vitamin D for more details. And keep in mind that correcting a Vitamin D deficiency can improve your immunity, protect from many diseases and condition, increase your energy levels and on and on. It is an incredibly important vitamin and will increase your long term health in a 100 different ways.
NOTE: Trying to correct testosterone levels through diet is still in its infancy as far as understanding in my opinion. There was one very old study that implied that going on a vegetarians diet could reduce testosterone levels by 30+%. However, a more recent study showed that vegans have higher testosterone levels than carnivores. See my link on Testosterone and Vegetarianism for additional information.
CAUTION: You should always treat low testosterone as a medical condition. In my book, Low Testosterone by the Numbers, I document how low testosterone is a risk factor for a host of nasty health disorders, including diabetes, Metabolic Syndrome, erectile dysfunction, osteoporois/osteopenia, weight gain, depression - the list goes on and on.
1) The Journal of Clinical Endocrinology & Metabolism, May 1 1988, 66(5):1019-1023, "Effect of Massive Weight Loss on Hypothalamic Pituitary-Gonadal Function in Obese Men"
2) Physiology & Behavior, Aug 1998, 65(1):59-62, "Testosterone changes during vicarious experiences of winning and losing among fans at sporting events"
3) Arch Sex Behav. 2011 Oct;40(5):921-6, "Salivary testosterone levels in men at a U.S. sex club"4) Clin Endocrinol (Oxf), 2008 Jun 25, [Epub ahead of print], "Effects of aromatase inhibition in hypogonadal older men: a randomized, double-blind, placebo-controlled trial"