With summer comes great weather, the kids out of school, and some desperate finagling with your schedule just to make it to the gym a few times a week. If this is the case and you've been lifting regularly your routine could benefit from super setting your workouts.
A superset is when you perform one exercise and then, without rest, move to another exercise that works the opposing muscle group. For example, if you're performing a bench press of 10 reps you would then move to a row and perform ten more repetitions. This will increase muscle activation without increasing the fatigue of either muscle. Think of it as a sort of tag team. Your chest rests while your back takes over. This is a great way to decrease on the amount of time spent on your workout while increasing the amount of work performed.
With a busy schedule you can still strength train twice a week and hit every part of your body in one hour sessions. Separate your days into chest/back and legs/core. The leg days are best to use core exercises between leg training exercises. My favorite is performing squats then moving into a 45 seconds of mountain climbers.
Whatever your routine remember to mix it up, listen to your body, and have fun.