1. Invest in Good Product
To ensure it doesn't look like you went in for a spray tan and asked for "tangerine", it's wise to use a good-quality self-tanner... it will be the difference between a believable glow, and a streaky, orange mess. I like St. Tropez Bronzing Mousse ($40), and Neostrata Insta-Tan ($26) for even results with nice colour.
2. Exfoliate
Before applying any type of self-tanning product, make sure to exfoliate all the areas you will be applying self tanner. Using a loofah or exfoliating gloves, pay extra attention to elbows and knees where product may build-up and give away your faking-it status.
3. Use a Mitt
Using a self-tanning mitt is a great trick to easily apply an evenly blend the right amount. This mitt will also prevent your hands from getting stained with tanner (another dead giveaway you weren't born with that J-Lo Glow).
4. Mix It Up
The average tanning product will give you a tan that lasts for about a week, but if you don't have time to religiously maintain the faux, supplement with other instant tanning products. A recent fav of mine is Sally Hansen Airbrush Legs. This stuff is amazing! So easy to apply, just spray into your hands and rub into your skin, and in 5 minutes you have perfectly tanned legs that last until your next shower. No transfer to clothing, no streaks, just a nice flawless colour. I have light-medium skin tone and I chose colour "tan glow".