One of the things I hate the most about watching my practice videos is all the times when I don’t keep my knees straight. Straight knees make a huge difference in having clean lines and not looking sloppy.
When you freestyle, check in on your inverts to make sure your legs are completely straight. You should have to really squeeze your quads to make this happen. Pointing your toes also helps. If you have a hard time getting it right, you probably need to do more cross-training to get leg muscles strong enough to squeeze your leg perfectly straight.
If you want some inspiration, check out this video of Zoraya Judd, starting at about 1:50. Perfectly straight legs, and even though it’s a simple shoulder mount it looks really dramatic.
Here are some more resources: