But I wondered how you know when to make the turn? Do you have a visual reference point on the runway? For example, you start the turn when you reach the second stripe after the centreline? Slightly crass analogy, but when you learn to drive and to do a reverse parallel park, you learn to turn when the car passes a certain point. Is it similar?
I suppose you could look at it that way, but I think you'll find that for most, it's a matter of feel; one knows how far to go based on one's own experience.
If one is entering the runway at a right angle to the runway direction, how far one goes relative to the far side of the runway really depends on how wide the runway is. Instead, if one goes a known distance past the centerline, swinging right or left to line up is a simple affair.
The process is more like driving a truck than taxiing a light airplane, particularly if one is sitting in the cockpit ahead of the nosewheel, instead of behind it. One goes past the turn point, then swings around to line up.
When I did my first day flight as a brand-new 747 First Officer, the training captain went outside, and set his flight case directly in line with the left main gear. He had me sit normally in my seat, and get an idea of just where the wheel would track in relation to my field of view. As it turned out, it's close enough that if one can see the edge of the runway out the window, then one isn't going to run off the runway. By doing this, the instructor was giving me a frame of reference for knowing where the gear was trailing along behind me.
When I first flew the PZL Dromader, I found that to swing onto a parking spot, putting the intended turning point just past the crook in the wing's leading edge would be ideal. In a J-3 cub, I could simply look out the window and put the tire on the spot and do the same thing. Swinging the tail became a matter of feel then, for how far the wings and tail would swing when parking.
Some of it can be done using a reference mark, and some of it is simply feel. How far one goes beyond the centerline of a runway or taxiway is also affected by the angle one enters the runway or taxiway. The larger the angle, the farther one must go past the centerline before tur ning...and of course it very much varies with the aircraft. For example, in the 747, the body gear trucks turn opposite the nosewheel, so that the turn radius is reduced, and the way in which the airplane turns differs from say, a C-130 or B737. Obviously taxiing a Cessna 172 is different from a Pitts Special or an Airbus A320. In some airplanes, one can follow the centerline stripe, whereas in others one can't, when turning a corner. One needs to understand what the airplane will do when taxiing, and this comes fundamentally from experience in the airplane and the training behind it.