Note: this is not a guide for budding actors and actresses, on how best to audition for the role of a companion on Doctor Who. If you are looking for that kind of thing, the best advice we can offer, based on the previous successful applicants, is to be entirely unlike the other ones, and to be good at raising a quizzical eyebrow.
The route into the TARDIS can be a surprisingly common one, if you happen to be (or have been) female, youngish, human and British during the last 50-odd years of Earth history. All you have to do is wait for an alien invasion of some sort, and keep your eye out for a big blue box. If you see one, chances are there will be an eccentric man somewhere in the vicinity, barking strange orders and running about.
Now, here comes the tricky bit, you need to make yourself useful to him, and sort of insinuate your way into his attention. This can either be because you need saving from the aliens and he can’t resist a damsel (or mansel) in distress, or because you’re in a position of authority and he needs you to do what he says right away. It might help to see if you can join your nearest branch of UNIT, or, if you’re a journalist like Sarah Jane Smith, just barge your way in and start asking questions until you and he are face to face.
What you need to do is be ready to be won over by him, be enchanted by his personality, and then occasionally bring his rampaging ego up short. It’s a bit like looking after a toddler, if a toddler had access to weaponised Lego.
Speaking of which, it does seems to help if you were cute as a child yourself. Don’t ask me why, but he does like to go back and investigate the past sometimes, and he loves children. If you were a spoilt brat, it might harm your chances.
Should you be reading this from some space-station in the far future, or a lost outpost near E-space, do not fear, there are other ways to make it into the Doctor’s affections, although you may have to wait a lot longer until you get your chance. The Doctor has a soft spot for waifs, strays and orphans, so if he’s around and you fancy a ride, try not to have too many family members hanging about, cramping your style.
There again, as Rose, Martha, Rory and Donna all demonstrated, sometimes he likes to feel part of a wider community. There are no hard and fast rules, he’s a capricious man.
Also, if you can, try and be the sort of person a TARDIS might like. I’ve no idea how you achieve this, but that blue box does just as much of the driving as her operator does, and she does sometimes materialise near to people she’s taken a shine to. Or they materialise in her, as Donna Noble did when she’d absorbed a few too many huon particles. We’ve all been there.
Oh speaking of Donna, you can sometimes find the Doctor by looking, if you investigate strange occurrences in your local area and keep an eye out to see if anyone else is too. Chances are it’s him. Take some Jammie Dodgers, he likes those.
Or you could do nothing. Sometimes you just get dragged into the Doctor’s slipstream by getting on with your life and not even being aware of his existence. Tegan was on her way to a new job and wanted to use a telephone to get help when her car got a flat tyre. Adric was running away from the Mistfall and needed a box to hide in. Peri was studying botany in Lanzarote. The only thing you need to be is ready, willing, and able to face down a Sontaran fleet or a rhino-headed policeman without collapsing in a heap.
As for the Doctor’s latest new friend, so far, she broadly fits all categories. Young, female, human (most of the time), abandoned on the Dalek asylum, good at sparring, a helpful and inquisitive professional in the midst of an invasion – even when it’s him, Amy and Rory that are doing the invading – and very quick with the quizzical eyebrow.
Good luck, and happy TARDIS hunting.