Typically, you’ll want to take Viagra 30 minutes to one hour before sexual activity, though it’s effective for up to four hours. Don’t take more than one dose of Viagra in any 24-hour period. Swallow the tablet whole. Don’t crush it up or chew it up. The tablets are designed to give you a predictable experience with minimum risk of unpleasant side effects.
Though Viagra can be taken with or without food, you should avoid eating a high-fat meal (like a cheeseburger and fries) when you take it, because this can cause effectiveness to be delayed. Take Viagra on an empty stomach each time if you want the most predictability about time to effectiveness.
Finally, in order to be effective for its intended purpose, sexual stimulation is required. Viagra isn’t designed to magically produce an erection out of nowhere, but rather to optimize physiological conditions so that you’ll have an erection while engaging in sexually stimulating activity.