In the beginning Sakura was annoying and nothing more than another Sasuke's fangirl, she also used to mock and mistreat Naruto. She was pretty useless too, she couldn't even defend herself. But in the Forest of Death arc she started to become more mature and she realized how much life was not a fairy tail and how much Sasuke wasn't some kind of enchanted prince, so her feelings for him grew up to an unwavering love, which is, in my opinion, her strongest feature and the driving force for her positive development. Since this arc a more kind and selfless side of Sakura is shown too, at the point she didn't even care for herself anymore, but only for Sasuke's well being. In the fight Team 7 had against Gaara, Sakura was almost suffocated by his grip of sand to defend Sasuke. Her relationship with Naruto developed too, she stopped mistreat him and started aknowledge him since he saved her from Gaara. When Sasuke left, Sakura realized how much weak she was and how much she couldn't do nothing to stop him, she also felt empathy for Naruto and decided to become stronger to help him in bringing Sasuke back. From part 1 to Shippuden she improved a lot, in the beginning she could barely defend herself, but in part 2 she was smashing the ground, punching things and healing people, not to mention that she defeated an Akatsuki member when she was 15 years old to find Sasuke, saved Chiyo's life, saved Kankuro's life, saved some people from Pain's monsters and healed half of Konoha during his invasion, defeated some clones, saved Naruto, saved Sasuke, punched a Goddess... if it's not some character development, I don't know what it is.
Her relationship with Naruto and Sasuke developed a lot too. She mistreated Naruto in the beginning, but started to really care and support him, one example is when she saved him during the war arc and did her best to not let his dream die. Her relationship with Sasuke too, she was just a fangirl, but then her crush became a selfless love to the point that she was willing to cross the hell to save him from darkness.
Sakura developed from an useless and annoying fangirl who liked to make fun of orphans to someone who has a selfless love, who truly cares for her dear ones' safety (including Naruto). She also became the best medical ninja in Konoha and saved many lives with her skills. She has a good heart and often shows her gentle side too, despite the fact that she is hotheaded and acts like a tomboy sometimes.
