What you shoot isn't necessarily what you post
Filters can make you more creative. Not only do Instagram filters have the potential to make your pictures look better, but the practice of using filters can get you in the mindset of editing almost all of your pictures. Before using Instagram I really never took the time to do any sort of post processing. I now do some sort of editing to almost all of my pictures that I share.
Square format can help you with creativity
The square format of Instagram does limit how much you can squeeze into a picture. However, the square format can also force you to think more creatively about how you compose a picture. Likewise, the square format can also encourage you to be more creative in how you crop pictures before editing and posting.
Practice makes you better
The more pictures you take, the better you can get with photography. It's often said that the Best camera is the one you have with you, and a mobile phone is always with you. While most phones today take some great pictures, it's important to understand that you aren't going to get dslr quality with a phone. Be content with what you can capture while on the go with your phone, and do your best with the camera's limitations. Sometimes the picture is more about how you frame the subject and use available light than the size of the sensor. Even if the picture you capture won't be good enough of a poster-sized print, what you learn in the process of framing, capturing, and editing the picture on your phone can help you with your “real camera” photography skills.
Sharing helps you learn
Instagram makes it very easy to tag and share your pictures and connect with others on Facebook, Twitter, or Flickr. It is also incredibly easy to find and follow others on Instagram. Connecting and sharing with others is a great way to learn from others and develop your photography and editing skills. Getting feedback and recognition from others when they notice one of your best shots is very rewarding.
While Instagram makes it very tempting to share every picture you take, try not to over share. Rather, only post your good, unique, or interesting stuff. I've taken tons of pictures I just deleted because no matter how I edited them or used a filter, they weren't worthy. At the same time, an interesting or unique photo that tells a meaningful story doesn't necessarily have to be a work of art.
What have you learned from Instagram? Has being active on Instagram helped you learn to take better pictures?