What other common ways are there to improve problem solving or creativity?
For problem solving, dwell on the problem in its domain just before bedtime, and make sure it's the last thing on your mind as you settle down into sleep. Let the subconscious have sole access to your understanding of the problem overnight.
Everybody's built different, but these work for me.
Has an interesting side effect of screwing with threshold of movement, particularly finger movement.
I play rhythm games (sifac, llsif, deresute, mirishita...) regularly and tried modafinil. My fingers wouldn't auto-move anymore, and furthermore even if I moved them consciously, it took more effort to do so.
At everything else, it puts caffeine to shame, with no tolerance buildup or withdrawal symptoms.