DIY Redneck Alignment

It's been a while since I owned a car that went in a straight line on its own. Every car I've had pulled to the right, which is normal on a 2 lane road that is crowned to shed rain water. But if I'm on the highway on a flat surface, I should be able to cruise in a straight line without touching the wheel. The correct alignment won't scrub off the sides of tires excessively and won't pull in either direction at all. Some cars have a centering bias due to either (rarely) an automatic hydraulic balancing system (like Citroen's DIRAVI) or due to suspension geometry. Forget about DIRAVI here.
Most cars have adjustable toe/steer. The mechanical linkage which sets the L/R bias of each front wheel is infinitely (finely?) adjustable within a few inches. The slack in the steering will determine the futility of these adjustments to some degree, but lets assume there's no slack, as all ball joints and steering linkage have been renewed. Caster/Camber are not adjustable here, and the spring rate and height are fixed also.
These would be fun to play around with, but ultimately would just make things handle worse unless there was a race track to try all the infinite settings out on.
I've seen many different methods of alignment using lasers, bubble levels, strings, beams etc... the basic point is to get all 4 wheels pointing in the same direction, so that there is no scrubbing, pulling, side tracking or crabbing.
In order to properly align a car, it must be on a flat, level surface. This is the basic criteria. The rear wheels are probably not adjustable for toe. The front wheels need to be on a surface that allows them to turn freely while loaded. The expensive alignment sets I've used had heavy steel platforms with big sealed roller bearings. They slip under the wheels and and turn freely. The cheap ones are pairs of steel plates with a point on one side that allows full toe/camber/caster adjustment. Lasers are attached to the wheels and used to point at gauges in the rear, which measure toe-in and toe-out.

Before "LASERS" were invented, people used string or long beams. An old trick was to grease up the back of a pair of vinyl tiles and roll the front wheels onto these.
Here's that method in detail:
http://mercedes-diy-alignment.blogspot.com/