I use the tape measure method.
Center the steerring wheel.

Pick a spot on the front of the tread and measure between the two tires.
Pick a spot at the rear of the tread and do the same.

If the rear measurement is larger you have toe in (front of the tires are pointing in-snow plowing). Crank the tie rods equally on both sides until the measurements are pretty close ( I go with about 1/8 inch toe in).

I measure with the front wheels off the ground and when it's back on the ground. I adjust when the wheels are off the ground.
Between adjustments, I lower the car, move it frontwards, then backwards about 15 feet, to settle the suspension, then recheck the measurements.
Recheck that your steering wheel is still centered. Drive it.

Some grease sandwhiched between two sheets of metal under each front tire can allow you to park the front wheels on them and do the adjustments with the car on the ground, but I don't do it.

If you're looking at the front of the car and your tires are leaning inwards at the top 45 degrees, then you have something else going on, as others have said.