As this is such an essential subject, there may already be a
"THIS IS THE ONLY CHAIN THREAD" thread, but here is a starting point:
How to Maintain and Adjust Your Motorcycle Chain - Tips on How to Take Care of Your Motorcycle Chain
This will get you on the right track.
But here is an idea that I like:
To make sure that you keep the rear axle perpendicular to the axis of the bike,
COUNT the turns you make when adjusting the chain, and be sure to make
exactly the same number of turns on the other (right in this case) side.
As you make this adjustment with an Allen key,
count the turns in sixths of a complete rotation.
Adjust the left: one sixth, two sixths, three sixths ... then do the same on the right.
When the turns are exactly equal, check the tension.
If you have made the chain too tight, back off equally on each side.
If you ever lose count, your rear axle may get away from perpendicular to
the direction the bike is going. When you see a motorcycle (or a car for that
matter) proceeding like a dog, angled to its direction of travel, then the
alignment is off, and it can be troublesome to get everything aligned right.
After all, If Mrs. Suzuki originally aimed us right, and we keep aligned,
we ought to stay properly aimed for ever, right? Just hope that whoever
services your motorcycle doesn't screw up the alignment.
That never happens, does it? Naaaaaaaahhhhhh.
I have been messin' with chains for 50 years, and it's still fun.