Two very popular training principles that are rooted in the past are Supersets and Compound Sets!
A Superset is when you do two exercises back-to-back for opposing muscle groups, without rest. For example, if you did a set of barbell curls for biceps and immediately followed it with a set of cable pushdowns for triceps, that would be one superset. Biceps and triceps, chest and back, or hamstrings and quads are the popular opposites for supersets. They can add different level of intensity to your workout, enhances the pump to the entire area being trained, and can be a great time saver. Try to use the same weights and rep ranges that you would use for your normal sets.
Compound Sets are successive exercises performed without rest for the same muscles or non opposing muscle groups. Often confused with “supersets” compound sets can work for any muscle group, not just opposing body parts, or even the same body part which is how they are most commonly used. For example, if you did a set of shoulder presses followed immediately by a set of lateral raises, that would be one compound set. Like with supersets, try to use your normal amounts of weight and repetitions, although this is often not possible due to the nature of compound sets.
Both principles will add an extra level of intensity, focus, and pace to your training. If used for larger muscle groups like chest, back, and legs, they will also add a cardio conditioning effect as you fight your way through the two movements before resting. Give them a try if you want to switch things up a bit, and remember to always warm up first, use weights you can handle safely, and utilize good form!