A quality bra can make them look good in clothing. In most cases anyway. Wacoal is really good and other bras in that $50—$70 price point. What size are you?
If you are heavy, losing some weight and building up the muscles behind the breasts can sometimes help a little, but the tissue in the breast that is not muscle cannot be repaired when it’s damaged. You can’t exercise it back into shape.
Don’t jump or jog without a good bra on. Never do a shimmy shake of the breast like Brazilians at carnival. These things damage the tissue that cannot be repaired. Tell young women.
Breast surgery is the only way to really perk them back up and have them be in a lift position without a bra.