I'm at a part in life where I need to make presentations at school, go to meeting and job interviews, and that mean to drees up more formal. In such cases I like to go for a T-shirt -blazer combo. The blazer sends a professional vibe, yet the T -shirt is more relaxed. I also I prefer to wear flat shoes, but that does not mean boring shoes. You can choose shoes with a cool texture or special decorations, which will raise the outfit several levels up. Speaking of decorations, do not forget the accessories. When everything is formal and polished you can play with interesting necklaces or statement earrings. But it's important to take it moderation, you do not want it to take the minds of the people in front of you while you talk.