Depending on your particular goal or sports activity there are limitless ways to structure a strength training routine. Bodybuilders like to TRY and isolate particular muscles (I don't really think you can ever isolate a muscle), powerlifters stick mainly to the power lifts and accessory lifts, and athletes work movements that will enhance athletic performance by mimicking the same movement patterns of their sport. At times this can be an extremely complicated process and there are people who get paid lots of money to design routines for top level competitors. But just because it CAN be complicated doesn't mean that it HAS to be. If your goal is to lose weight, maintain health and longevity, improve fitness, or simply look good in a bathing suit, then a simple and effective routine is all you need. So here it is:
This template is based around basic movement patterns that when put together will stress every muscle in the body. Muscles do not know what exercise you are performing, they just know that they are contracting and your body is expending energy. So if you just perform certain movements the muscles will take care of the rest. And, those movements are push, pull, and squat.
The push movements effectively work the chest, shoulders, and triceps. If you do this exercise with enough intensity than you do not have to worry about doing three different shoulder exercises and five various triceps exercises. My favorite options for the push category include push-ups(and all their variations) and dumbbell shoulder presses.
So there you have it. Those three different movements are all you need to get in an effective strength training routine. Now, let's talk the specifics of performing your routine. You should do strength training on at least two, preferably three, days per week. Space the days out so that you have a day of recovery in between workouts. On the "recovery" days you can do other activities just limit the strength based activities. Since there are two options for each movement I would alternate the movements in each workout. That way you are performing a variety of movements and avoiding overuse injuries. As far as set and reps, start out with 2 sets of 10-15 reps, and as you progress you can build up to 4 sets of 5-10 reps. Just make sure that you are challenging yourself and working at a high intensity( not just going through the motions). So a simple, basic routine would look like this:
Monday: Push up, Inverted Row, Goblet Squat : 2 sets, 12 reps each exercise
Thursday: Shoulder Press, Pull Up, Walking Lunge: 2 sets, 12 reps each exercise
Remember, this is a basic beginner routine. If you have been strength training for a while you can still use this template, but you should add more movements, add more sets, and use heavier weights. Good luck.