This isn't the only way, maybe not the best way, but its what I use and it works great for me.
There is a vertical weld on the swing arm close towards the front of the swing arm. Take small ruler and pull the chain up as hard as you can directly above that weld. If measurement is around 45mm or 1 3/4", my chain is tensioned correctly (tx alvis).
There is also a detailed way in your operators manual;
Drive Chain Slack Inspection
○Check the slack with the motorcycle setting on its side-stand.
○Clean the chain if it is dirty, and lubricate it if it appears
•Check the wheel alignment (seeWheel Alignment Inspection).
•Rotate the rear wheel to find the position where the chain
is tightest. •Measure the vertical movement (chain slack) [A] midway
between the sprockets.
If the chain slack exceeds the standard, adjust it.
Standard: 25 ∼ 35 mm (1.0 ∼ 1.4 in.)
Drive Chain Slack Adjustment •Raise the rear wheel off the ground with the stand. •Remove the cotter pin [A], and loosen the axle nut [B]. •Loosen the both chain adjuster lock-nuts [C].
If the chain is too loose, turn out the right and left chain
adjusters [D] evenly.
If the chain is too tight, turn in the right and left chain
adjusters evenly, and kick the wheel forward. •Turn both chain adjusters evenly until the drive chain has
the correct amount of slack. To keep the chain and wheel
properly aligned, the notch [E] on the left wheel alignment
indicator [F] should align with the same swing-arm mark or
position [G] that the right indicator notch aligns with.
Misalignment of the wheel will result in abnormal
wear and may result in an unsafe riding condition.
•Tighten both chain adjuster lock-nuts securely. •Tighten the axle nut.
Torque - Rear Axle Nut: 108 N·m (11.0 kgf·m, 80 ft·lb)
•Turn the wheel,measure the chain slack again
Most important thing you can do for your chain once its correctly adjusted is lube it every 300-500 miles. Mine has around 11k miles on it now and other than when I put the 16tooth sprocket on it, its never needed adjusting.
The adjuster lock nuts are 12mm, if you have two 12mm wrenches its much easier. The axle nuts are 22mm & 27mm, not in your typical socket set. If you are thinking of getting some, buy the six sided black impact sockets, not the chrome multi-sided ones. Most of the V's nuts and bolts were over-torqued by some over sexed gorilla that didn't know his own strength.