I also enjoy lifting. I wear a heart rate monitor and start the next set as soon as my heart rate drops to 100. If I'm out of shape, I'll make that 110, because it takes too long to reach 100. That saves time and makes the workout somewhat aerobic. I make sure I've eaten something 2-3 hours before a workout, either bike or weights, and then have some sort of carb/protein recovery drink immediately after. I sip a sports drink during the workout so my blood sugar doesn't drop out. I never allow myself to get starving hungry. I like to workout right after work, before dinner.