Step 1: Pick something you like.
Step 2: Think of as many ways as possible to make it better, more efficient, more durable, cheaper, longer lasting, more entertaining et cetera.
Step 3: Which solution from step 2 are your skills or connections the best fit for?
Step 4: Find inexpensive way to put prototype in front of potential customers.
Step 5: Note feedback from step 4 and iterate.
Step 6: Profit.
(Step 7: Contribute.)