First up - I commend you on your wish to draw better boobs! As a haver of boobs, I always appreciate more realistic depictions of them.
And as you say, you have some work to do, because these ladies look a bit as though they have helium-balloons strapped to their chests. They also seem to be suffering from a bit of the boob-sock syndrome in the wardrobe department - unless dragonfly lady and the girl with the cape have clothing with specially sown individual pockets for each of their breasts in their clothes, their boobs would not, actually, look like that when wearing clothes.
Even assuming they're wearing some kind of sturdy sports bra for support, their boobs would not be individually visible like that. This picture is of a woman with a sizeable chest wearing a sportsbra - and if your girls are going to be doing ANY running and jumping, they're probably going to want to wear one of them - and as you can see, it does not show off her breasts in individual boob-socks.
I did a quick draw-over of your picture here - first I just did a sketch following your exact lines, then I did my own version adjusted with more realistic anatomy, and then I did one with suggestions for how to draw clothes on top of that.
The anatomy adjustments mostly involve a.) giving them ribcages wide enough to support that kind of weight, and b.) letting those boobs relax a bit. Even IF you're going for the gravity-defying superhero helium-boob look, breasts have weight. Unless you construct some kind of undergarment with a hard plastic shell or something, they're going to be affected by gravity somehow. Let them actually rest on the ribcage underneath them, and that'll go a long way towards making them less helium-balloony.
Also, a few small non-boob-related notes.
Most people do not have that much space between their thighs. A lot of supermodels do, but the rest of us tend to carry a bit of fat around in our thighs even at the best of times. The dragonfly lady's thighs would probably not have that kind of gap if she were real. Just a thing to keep in mind!
The lady on the far right has something funky going on with her pelvis. The way her pelvis, torso and legs fit together looks a bit weird in your original drawing. Part of it, certainly, is the way her hips are much narrower than her shoulders. Some women DO have hips that are narrower than their shoulders - the human body comes in infinite varieties! - but in this case, the difference is a bit TOO big to work.
The lady on the right also has no navel. I know it might be tucked in under the waistband of their tiny skirt, but, uh, that's a bit too low. My navel sits level with the top of my hipbones; if you've pushed her navel down that far, it's getting a bit too close to her lady-parts for comfort.
The green lady's chest-covering is not functional. Unless that is just paint instead of cloth, it simply would not work. She'd be able to take maybe two steps before her breasts slipped out of it and the fabric was bunched into her armpits. There's a reason most bras and bikinis fasten to a band underneath the breasts; it's to keep it from slipping around. In my costume-suggestion drawing, I've added a string beneath her boobs for the fabric to fasten to.
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Basically, the best way to learn how to draw better boobs is to draw from life. If you don't have access to a lifedrawing class, use your google-fu to find pictures of people with boobs - with or without clothes, because as mentioned, the clothing on these ladies serve to amplify the impression that your drawn boobs aren't quite working.
Good luck!