If Marvel want to start laying further groundwork for Doctor Strange's solo movie being released in November (am I the only one who can't freakin' wait?), a good place to start would be Civil War. Don't forget, the first mention of the character occurred in The Winter Soldier, so there'd be a theme here. All you'd need is Strange chilling at home in Greenwich Village with Wong - he's already a person of interest as far as Winter Soldier, which means that he's had his magical powers for a couple of years at this point - watching the events of the Civil War unfold at home, before potentially deciding to get involved. Hey, if they're going to ram Spider-Man in with a minor amount of set-up, they could definitely have Strange turn up for the big final tussle which firmly brings him into the wider purview of the MCU - with the added benefit of giving him existing relationships with the Avengers by the time Infinity War arrives.