Academically called the T/C Ratio, the ratio between your Testosterone and Cortisol levels will help determine your mental, and catabolic-anabolic states.

At low levels of Testosterone, men experience increased fat growth, decreased libido, decreased aggressiveness, decreased mental drive, less body/facial hair growth. Low T predisposes a man to a catabolic muscle building environment (read: muscle wasting environment) and Beta mentality at an autonomic level. With high T, a man grows muscle quicker, gains fat more slowly or loses fat more easily, gains a deepened voice, grows more body hair, grows more bone and even develops a more aesthetically pleasing facial bone structure.

At high levels of Cortisol, men experience Reduced glucose utilization, Osteoporosis, impaired immunity, reduced muscle mass, increased abdominal fat. High Cortisol pushes the body into a catabolic and mentally strained state as well. The two hormones are linked where the presence of one "opposes" the other (simplified). Further, high Cortisol includes anxiety, stress, decreased energy levels -- mental debilitators that will make going and doing (the traits of a self-actualized and "Alpha" man) harder and less natural feeling. It will use more of your valuable willpower to get off your ass and do the shit you ought to be doing. See the introductory paragraphs of this research review for more

The answer then is to optimize your T/C Ratio to keep your body in more anabolic state and your mind in a more alpha state. The first step is to do everything in your power to naturally increase your baseline Testosterone levels. This has been covered here on this sub before so I will not go too in depth, but this is the most important step of the process. The lifestyle changes it involves are ultimately good lifestyle choices anyways beyond mere testosterone. This guy increased his testosterone nearly 100% over 90-days, proven in bloodwork. It is my opinion that increasing testosterone to your natural maximum or getting on hormone replacement if necessary is the single most important step down the RP path. Consult other posts here on TRP and the Art of Manliness link above for more detail on Testosterone. The next step in that journey, and the focus of this post, is to control cortisol to optimize the back-half of the ratio.

Meditation and Mind Body Connection

Power Pose

As pointed out by /u/bookhockey24, merely holding a power pose for 2, 1-minute sessions leads to a 13% increase in Testosterone and a simultaneous ~20% drop in Cortisol. In fact, the psychological effects of this pose have been evaluated and shown to increase social dominance and leadership qualities -- alpha traits. Research Review here. Incorporate the victory pose into your routine.

Meditation

Meditation has been covered in great detail elsewhere in this sub. It is highly beneficial, and you should be doing it. Physiologically, post-workout meditation can eliminate the small workout hit to Testosterone, reduce post-workout Cortisol response, and increase post-workout Growth Hormone production. Meditation can be used to directly drop Cortisol levels up to, 30-40% according to a 2002 study.

Massage

One study noted a 31% decrease in cortisol, and similar increasing in dopamine and seratonin, following a massage. Source. However, other research isn't as enthusiastic about the cortisol reduction properties of massage, like detailed in this research review. The studies do agree massage has statistically significant anti-depressive and anti-anxiety effects.

Anti-Cortisol Supplementation

Ashwagandha

Ashwagandha is a multi-hitter -- the research supports that it directly addresses anxiety, cortisol and testosterone in a single herb. Dose this at 6,000 mg split 3 times a day. It has been shown to positively impact the HPTA to increase testosterone in infertile men. Don't expect this to boost your T if you are a fertile (non-hypogonadal), normal man. More importantly, it has direct anxiety reducing and anti-depressive effects in chronic stress situations (e.g. non-medical, day-to-day stress) contributing to a better mental state. Finally, it's been shown to reduce Cortisol 15-25%. Sources

Vitamin C

Vitamin C is not a general cortisol reducer. Most clickbait sites will tell you it is. It is not. However, taken immediately post-exercise or intra-exercise in doeses of 600-800mg, there is some support for cortisol reduction here.

Fish Oil

Fish oil is something you should be taking anyways, but it's shown to have a small but statistically significant cortisol reducing influence. Source

Less well studied anti-cortisol supplements

11-Oxo

11-Keto (aka 11-Oxo, aka adrenosterone) 11 OXO works by blocking an enzyme called 11-beta-hydroxysteroid dehydrogenase type 1 (11-BHSD I). By blocking this enzyme, 11 OXO suppresses the undesirable actions of the hormone cortisol on specific target tissues in the body. It was recently banned in the USA, but may still be legal in other countries.

Phosphatidylserine

This compound is shown to have neuroprotective and cognitives benefits in addition to cortisol reduction properties. However, only bovine cortex sourced Phosphatidylserine will get you the cortisol reduction effect -- soy based (which is almost certainly what is sold OTC) has been shown to have no effect up to 750mg. Source

Unstudied anti-cortisol supplements, approach with more caution

7b-hydroxy-17b-dihydro DHEA

7b-hydroxy-17b-dihydro DHEA (aka 5-AT) is structurally related to 11-oxo but is not very well studied at this point. This is found in bodybuilding supplements like Lean Xtreme. It may reduce cortisol

NOTE

EDIT: Despite that the section on supplements is longer, my advice is to focus first on the lifestyle tips in the Art of Manliness Link above and here, then focus on the meditation aspect, then lastly consider supplements.

In my experience you get 80-90% of the effect from lifestyle (eating/lifting/meditation) and the last 10-20% from supplements.