Collage is the time when you experiment with your dressing. There is a thin line between looking ugly and trying new trends.
I would suggest you to go for clothing which you are comfortable wearing. As you mentioned simple and smart, I will list some categories which you can mix and match according to your preference.
Tops:
Go for a correct fit,bright colors, different prints.
Graphic t-shirt (there are many fun prints available) you are not revealing your body but you look smart.
Tank tops, blouses, shirts (half sleeve, full sleeve), kurtas (try new ways to match a kurta with).
Bottoms:
Go for correct fit, different colors, little thicker fabric.
Jeans(try different wash and fits) go for a little stretch.
skirts (try different lengths), wrap arounds, pants other than jeans (cargo pants, cotton/linen/corduroy pants).
Loose pyjamas:
You can team this with a graphic t-shirt, flip flops, patiala pant with different t-shirts. It is ultimate comfort.
Dresses:
I personally love dresses/frocks. You can look for different lengths, prints, fabrics, sleeve less/half sleeves/full sleeves, wraparound etc.
With all the garments, mix and match simple accessories like a watch, a bracelet, ear rings, finger rings. Pick comfortable footwear. Reserve heels for special occasions.
Try some looks and let me know how you like them. Let me know if you need more help.