i'm looking for basic tips which can help to improve your drawings. Share them here!
Thanks in Advance

read up on or watch painting/drawing tips online, If you have art academy try out some of the lessons and the last (and the most important one) practice.
It's also important experiment by mixing colours, trying different strokes and watch how other people draw their pictures using the Colors! 3D gallery.
I hope I've managed to help.

I've learned a lot from watching replays of the top paintings in the colors gallery. Just play them on the slowest setting possible. Sure, it'll be very long but you'll see how to get certain effects like texture or shading step for step. I also often downloaded the paintings I liked so I could zoom in to see the details how they made their textures like cross-hatching etc.
It's even better when you watch the replays on your computer (http://colorslive.com) because the image will be larger and you can simultaneously try out the methods you see on your 3DS.