My projects are usually a solution to some problem so I usually go looking for problems.
Whats a problem at work?
In your personal life?
What do you not like doing?
What repetitive task do you do a lot?
Where do you spend your time and what on?
Anytime you think why.
Look on stack overflow if there is a problem that keeps coming up its because the solution isn't good enough.
Here and on reddit I look at what other people are complaining about, or excited about.