Vinyl Engine is a great resource.
Essentially you need to decide what sort of alignment you want to go for (if you aren’t inclined to get into all that, just go for Baerwald) and then find an alignment protractor on the link provided by Ugg10 corresponding to the effective length of your tonearm.
You can print it off (make sure it prints 1:1 scale!) and very carefully punch a hole where marked, so you can fit it over your spindle.
Remove the power supply from your turntable to prevent any accidents...
The alignment protractor will have the null points marked on it, 2 of them, each within a set of grid lines. It should have a guide-line that has to point at the the exact centre of the point where your tone arm pivots, then you know that the protractor is perfectly positioned. You need to loosen off the cartridge bolts in the headshell (loose enough so that you can just about move the cartridge about, but tight enough so it stays where it is if not being deliberately moved - you may need to loosen a little and partially re-tighten for each little tweak)
Then carefully try to place the stylus on the first null point. If it doesn’t quite line up then raise your arm and move the cartridge back or forth as needed until it lands precisely on the mark. Then see if the cartridge body lines up with the grid lines. If not then raise the arm and twist the cartridge slightly as needed, and lower again. It should be absolutely square to the grid lines. If your cartridge is an annoying one without parallel sides, then just go by the front and make sure it’s perfectly parallel to the lines.
Once you’ve got it perfectly aligned on the first null point, then move over to the second. It should also be perfectly aligned to that. If it’s not then check that the spindle guide line is perfectly aligned To the tonearm pivot. You may have to shuffle back and forth between the 2 null points iteratively tweaking the cartridge alignment until it’s perfectly aligned on both null points.
Once it is then very very carefully tighten up the headshell bolts ensuring that you don’t accidentally move the cartridge as you do so (possibly the hardest part). If you do then you need to start again.
It’s a fiddly old job. Don’t try to do it in a hurry. I’d say set aside an hour so you can take your time.
If you don’t mind spending a bit of money, then this is about the best in the business, offering a choice of alignments, can work for any tonearm effective length (within reason) and it makes the whole thing a lot quicker and easier. It only has one null point marked because it’s impossible to mis-align the protractor itself.
Clearaudio High Precision Cartridge Alignment Gauge This Alignment gauge is a must for anyone serious about setting up their turntable properly. This Gauge is machined from solid aluminium with engraved markings. This gauge makes setting-up of any pivoted tonearm a breeze. IMAGE SHOWS ALIGNING...
www.analogueseduction.net
The picture shows the older version, make sure you get the one with 4 different alignments on it.
Hope that helps!