I am always telling you guys things you should do during your next workout, but here is something you shouldn't do: Hold your breath while weightlifting.
It may sound strange to remind you to breathe, but many of us have the tendency to hold our breath during the strenuous part of a lift. The problem is that breathing improperly while lifting can increase blood pressure potentially leading to light headedness, dizziness, nausea, hernia, heart attack or even stroke. Holding one's breath can be especially problematic for someone with hypertension or already elevated high blood pressure. To avoid this, inhale with eccentric (the easy part) and exhale with each concentric phase (the hard part - when the muscle you are working is shortening) of a repetition. However during cardio, no need to get fancy, just breathe naturally.