I'd advise against using hyperventilation if you want to produce stable unconsciousness. When fainting is partially or entirely caused by a lack of CO2, the effect of hypocapnia disappears when CO2 builds up. You need to displace oxygen from the lungs to produce hypoxemia which can be reverted only by inhaling fresh air with enough oxygen. If you pass out too fast due to combination of hypoxemia and hypocapnia, there is a risk of getting insufficient hypoxemia that wouldn't be able to maintain unconsciousness when hypocapnia stops working.
Inhalation procedure is straightforward. You should fully exhale, wrap your lips around the nozzle of the can, push the trigger and inhale the gas until you fill the maximally possible volume of the lungs. You shouldn't tilt of flip the can. You should also avoid inhaling air through the nose or exhaling the gas through the nose. A single deep inhalation of the asphyxiant followed by breath-holding can be enough for producing unconsciousness in nearly 30 - 40 seconds, but you can fully exhale the gas mixture from the lungs and repeat inhalation for better reliability.
Some people use air dusters to produce fainting before drowning or hanging. This makes sense, because drowning or handing may be unpleasant otherwise.
The irritating strength of the odorants in air dusters varies depending on manufacturers. It makes sense to avoid any manufacturers which are known for participating in campaigns against inhalant abuse (f.e., cans sold under brand "Dust-Off" are probably among the worst), buy cans of different brands, and choose the best one. Vomiting from inhaling such gases is very unlikely, unless you inhale a lot of gas in multiple passes.