Question

what is an innovative idea which is useful for our society ? ...

Answer 1

It's not an exact science, and having an innovative idea doesn't come so easily. It's a mindset and also a hard work. You can start by thinking outside the box, applying some creativity methods, and then find a design challenge.
For changing society, i recommend you the "Human centered design" (HCD) process, which is a process for designing solutions that answers human needs...

Answer 2

hey..
as we all know that innovative ideas are one who can change our life.. mind... and may be complete society...
so first is ....
Fun caution signs shaped like slippery bananas. These signs certainly grab our attention more than the standard ones........
I have only one idea at this time...