There are countless ways of earning money online profitably, but to make them effective for you as an individual you need to streamline them down to what really interests you.
And if you have time on your hands maybe you are still a student or something like that you can try out as many ventures as possible till you see the one you really like and is profitable, then focus your energy on that thing alone.
For starters I'll advise starting a blog, registering on pay to post websites and selling of domain.
At least they don't require rigorous efforts like others.