When trying on a bra, there should not be a gap between the strap and the cup. Your bra straps should lay flat across your breast. This can be an indication that your bra straps are too loose or that the bra is too big.
Your boobs should not be spilling out at the sides, this means that your bra is too small and you might need to go up a cup size.
Also On Majic 102.1: