Not Medical Advice: To get an even, all over tan, TipsForTanning.com suggests that you should lay on your back for 20 to 30 minutes, then flip and lay on your stomach for another 20 to 30 minutes.
The best time to tan to get an all over tan is when the sun is the strongest, between 10am and 2pm. Because the sun is directly overhead during these times, you have the best chance of getting an all over tan.
Laying out on a reflective blanket is a great way of getting a tan all over. If you are lying on a reflective blanket, the suns rays will reflect up allowing you to get tan on your sides.
After a few days, you can gradually increase the amount of time you lay on each side. This will prevent a sunburn.
Check out more helpful tanning tips here.
And here are 7 tricks and tips for getting the best sun tan safely from Cosmopolitan.