At the end of your hard weights session if you are keen to improve your fitness, aid in recovery and burn some fat then add 3-5 sets of intervals, i.e, 2 minutes on one minute rest x 5 sets. If you have more fat to burn then do up to 30 minutes pending on time spent in gym already and how you are feeling.
The science is that your body will learn to buffer lactic acid, which is the build up of waste product in the muscle when no oxygen is present during exercise. Therefore, next time you train your body will be fitter to deal with each set and you should need less recovery between your sets and have a higher output. This will lead to better muscle gain as your hormone release will be greater and this will feed your muscles.
So add a few sets at the end of your sessions. If it is just for recovery and fitness improvement then keep it to 5 minutes and if it is for fitness and fat loss then up to 30 minutes.
Finally, you need to exercise the same muscles you did in the workout i.e, leg day do cycling or skipping, upper body day try skipping or boxing!
Next time you watch your recovery between sets improve!