One night while complaining to a friend of not having a major enemy or cause(what are heroes without something to battle?), I said maybe something like this could happen, then this, and then... And I had figured out the primary conflict in 5 minutes of complaining about not having anything.
Other ideas come from seemingly unrelated events. Last night at 3:30am as I was watching the Perseid meteor shower I got the idea for my secondary conflict.
You never know where ideas will come from, but you have to be paying attention when the first little sparks ignite.