Tools you will need:
24, 14, 12 mm wrench

The official method is, to check chain tension while the bike ist resting on the sidestand, with no load. Chain movement has to be (as told by Honda) 3.5-4.5 cm, measured in the middle of the lower run of the chain. Movement is from most bottom to most top. IMHO, 3.5 cm is definitely too less, i.e., chain is too tight. I normally adjust my chain to appr. 4.5 cm.
Loosen the 24 mm rear axle nut, loosen the 12 mm securing nuts on rear of the tensioners. While loosening them, hold the 14 mm adjusting screw. Now begin adjusting with the left tensioner. Adjust chain tension by turning adjusting screw, and counting any eighth turning of the nut (clockwise=tighten, counterclockwise=loosen). When chain tension is good, proceed with the right tensioner. Turn the screw by the same number of eighths as the left one. Check chain movement around the whole girth of the chain. Check, if wheel is running straight, or if both sprockets are in straight line, respectively. This is done most exactly by measuring the distance from middle of swingarm axle nut to middle of rear wheel axle nut. Has to be the same on both sides, of course. Tighten all nuts (donīt forget securing nuts ... ). Finally, check chain tension under load, ideally at that point, where front sprocket axle, swingarm axle and rear wheel axle are in one line. This is the point of maximum chain tension. Free movement should be appr. 1.5 cm at this point. Check and adjust rear brake lever play (drum brake only).

For long durability, a chain has to be cleaned and lubricated regularly. Also an o-ring chain, having it's on grease inside it's roles. But to prevent friction between chain and sprockets, it has to be lubricated. When using an o-ring or an x-ring chain, be sure, the lubricant is o-ring safe. Don't use any stuff like that old-fashioned chain grease, coming in big flat cans, by Castrol, f.e. This grease you have to warm up, put the chain into and "boil" it. It's probably the best you can do to a non-o-ring chain, but it will damage the o-rings. Probably the best chain spray is a teflon (PTFE) based one. Chain has to be lubricated at least every 500 km or more often, depending on environmental conditions (heat, rain ...). Best check lubrication at any fuel stop.
Spray the inner part of the chain (i.e., the one being in contact to the sprockets) on the lower run. Spraying outer part, makes no sense, since lubricant won't reach the sprockets ... Wait some 15 minutes before riding off, to give solvents the chance to evaporate.
Before lubricating, you may want to clean the chain. Don't use fuel for this, best stuff for cleaning is paraffin (kerosene, Petroleum in German). The second best is Diesel fuel. Use a brush. BTW, there's no need to remove chain for cleaning.

There's a little sticker on the left side of the swingarm (1), coloured either blue or green/red. As long as chain tensioner's indicator (2) is pointing inside the blue/green surface, everything is ok. If it surpasses the right (back) edge of that surface, chain and sprockets have to be replaced. At least, the manual is reading like that ... IMHO, this is kinda commercial indicator, normally you can ride at least another 1,500 or 2,000 km.

However, there are some certain signs, telling you, that your chain set (always replace chain and sprockets!) has to be replaced: