The most common way of not getting a hit (aside from not producing any smoke at all, but that's fairly obvious) is leaving it in your mouth or throat rather than getting it to your lungs. The above suggestions are good. The simplest catch-all solution for this problem is just to breathe normally for a second after taking your hit - do whatever you normally do to take a hit, then breathe in a bit. This will pull in any smoke that hasn't yet made it down to your lungs, delivering its lovely payload of THC.