What is the best way to increase the libido of a 27 y.O. Male?

Live healthy. Get 8hrs sleep and exercise 1 hr a day. Don't smoke or abuse drugs. If you drink, drink in moderation. Eat healthy. Oh yes, fall in love.
Decrease stress. Decreasing stress, diet, exercise, eating healthy, avoid too much alcohol, avoid tobacco in any form, avoid drugs, etc. Being with somebody you find sexually attractive and feel comfortable with is probably the most effective option.