The above tips are good advice, but let's start at the beginning...
First, the car needs to be "checked for square". Get it up in the air, either on a lift or on jackstands. Check to see if the rear end is centered under the car. This is done by measuring from the rear backing plates (or caliper brackets if disc brakes) to the frame rails at the same place on both sides. The dimensions shoild be within 1/8" (or less) of the same. If not, make the necessary adjustments before proceeding.
Next, check the rear end for square. To do this, find the center of the front crossmember and mark it. (On all the chassis I build, I center-punch a permanent dimple in the center of the front cross member so I have a permanent measuring point.) Now measure from the center of the front crossmember to equal points on the rear axle. This is easy on a bare chassis, but can be a real challenge on an assembled car with the engine, trans, etc. in the way. (An offset measuring device or "tram" would be helpful here. You might be able to borrow a tram from a body shop or you can make a temporary tram from a long stick, a couple of sharpened dowel rods, and two pair of Vise Grips). The two dimensions from the outer ends of the rear axle housing to the center of the front crossmember should be within 1/8" or less.
If the rear end is centered and squared, the chassis will go down the road straight without "dog tracking". Now we can move to the front end and set the alignment. Make sure the front axle is centered by measuring from the kingpins to the frame. Next, check the front axle for square by measuring from the king pins to the already squared rear axle housing. Make any necessary adjustments to get within + or - 1/16".
Now check for caster. Caster is the angle of tilt of the front kingpins as viewed from the side. If the top of the kingpin tilts toward the rear of the vehicle, this is POSITIVE caster. On some big heavy cars like old Cadillacs and Lincolns, the factories actually used NEGATIVE caster (kingpin angle tilted forward) so the cars would be easier to steer. It worked OK on those big old land cruisers, but on a lightweight car NEGATIVE caster will cause the car to wander all over the road. To check for caster, put the car on the ground on a flat, smooth surface (garage floor?) and measure the tilt of the front kingpins. This can be done with a degree level held against the axle at the kingpin location or you can use a carpenter's framing square and a protractor. We are looking for POSITIVE caster of 5 to 7 degrees. Less than 5 degrees will cause the front end to wander; more than 7 degrees will cause the front end to shake uncontrollably. I generally try to keep my front ends closer to 5 degrees. Caster is adjusted by turning the clevises in your radius rods in or out as necessary. To increase POSITIVE caster you would want to pull the top of the kingpin back, so you would screw the top clevise in or the bottom one out.
Finally, check the toe. It should be 1/16 to 1/8 inch in. Zero toe will cause the car to wander; toe-out will cause undue tire wear and may cause front end shake. If everything is set correctly, the car should go down the road straight and smooth. Take it for a test drive; get up to about 30 mph and hit a bump with one of the front wheels. If it begins to shake uncontrollably, either something is not adjusted correctly or some component is defective. If all is well, try 40 mph, then 50. If there is vibration in the front end at highway speed, you may need to increase the toe-in slightly. You can go up to 1/4" in if necessary (this is more prevalent in really skinny tires & wire wheels).
Sorry for being so long-winded here, but the front end is the most important component of any car...