Take some very generic, very simple, completely trivial and trite theme - something entirely unoriginal - and try to write it best to your ability... no, not even best, just adequately, correctly. Start writing it, and if your imagination is taking you places, let it.
Last week I started off with a Romeo & Juliet balcony scene knock-off. Yesterday it turned into Inception-like battle across multiple levels of dream between "The Romeo" and a succubus demon impersonating "The Juliet", with "the real Juliet" trapped and held hostage by the demon in the dream world (and not being just a generic passive damsel in distress either...)
Now, how to approach turning a simple scenario into a complex one: first, use some artistic liberties in execution. Stylization, mood, change of events. Sooner or later your modifications will create errors; characters acting out-of-character, time dependencies broken, enemies acting like idiots, suspension of disbelief shaken, things coming out easier than they normally happen in life, little inconsistencies. Don't correct them! Embrace them and modify the behind-the-scenes circumstances to fit the bill. Hidden agendas, foreknowledge, utter negation of events. Then let the story flow with the new motives, and their (dire) consequences.
So, my Romeo sneaks through the gardens to his Juliet, then meets her. She's totally out of character, far too sexually aggressive, dominant, demanding. I'm just about to scratch that when I recall: The gardens are guarded by quite an elite of security. What are his chances of sneaking past them? About none. So, no, he didn't get there at all. He got shot with a tranquilizer a third of the way in, and he's dreaming currently. And the out-of-character, sexually aggressive Juliet is not Juliet at all. Moreover, he notices that! Our protagonist did have an event involving some nondescript mighty enemies in the past. So let's adapt the reality, pick a sexually aggressive, powerful enemy. The lore suggests a succubus demon fits the bill, let's run with that and solidify the nondescript past enemies into demons, with the succubus as their leader. So, do we get through the story without the real Juliet? No way. She's in there, pulled into the dream by a quirk of the lore. For now it's a quirk, but it will earn significance later.
Given these premises, this set of conditions, this conflict, let's roll with the battle, sides taking turns in the battle, hitting the other where it hurts, seeking inner strengths where it matters, losing and finding faith - we got the action story in full flair. We just report the progress of events, it's bound to take us to an interesting conclusion no matter how it goes.
That way two gaping plot holes (incompetent security and OOC protagonist) in a clear-cut run-off-the-mill cliché get transformed into an interesting premise.