You can apply lemon juice directly to the skin using your fingers or a cotton pad. However be aware that lemon juice increases your skin's sensitivity to sunlight, so wait for it to dry on your skin before going out in the sunlight and be sure to apply an SPF!
If you don't fancy going down the raw lemon juice route, try One Love Organics Morning Glory 30ml ($59.00 oneloveorganics.com) - a powerful serum that contains organic lemon balm. This complexion booster helps to de-puff and protect the skin, as well as brighten the shit out of it! I love this stuff.