Summarize this article:

If you were blessed with full breasts, make your cleavage pop even further by wearing a t-shirt in a v-neck, plunging or sweetheart cut. Make sure you’re wearing a well-fitting bra underneath your shirt to prevent spillage.  If your breasts spill over the tops and sides of your bra, it’s time to get remeasured. Breasts should be lifted and separated when wearing a V-neck top. If they are too squished together, opt for a different bra. Working out your pectoral muscles as you’re getting ready can actually make your breasts look larger. To work out your pecs, grab two 20 oz water bottles and lie down on your back. Extend your arms to the sides to make a T shape, then lift your arms to meet over your chest.  Keep your knees bent and your feet flat on the floor. Do 25 reps a day for a noticeable lift. Sleeping on your stomach may cause wrinkles on your chest. Try to sleep on your back or side whenever possible and apply sunscreen and moisturizer to your chest if you’re planning to be in the sun. To further improve your breasts as you sleep, wear a sleep bra to bed. The sleep bra will help prevent your breasts from sagging long-term.

Summary:
Wear the right top. Lift your breasts through exercise. Sleep on your back.