The general philosophy for any sensible workout plan is more or less this: it should be challenging, cover all muscle groups, have some progression (changes with time) and be relatively short (1-1.5 hours). Let me expound on these further. Challenging workouts are engaging and make you push yourself in the gym, which in turns leads to progress. Balanced workout covering all muscle groups are a good idea unless you are trying some advanced deconditioning methods (working harder on certain muscle groups while holding others constant) or recovering from an injury. This means, working out your back and legs as much as you would train your mirror muscles (arms, chest and abs). Reason -- training these large muscle groups using compound movements (that recruit multiple muscle groups and joints) also increases testosterone production, which has several health benefits including muscle gain and fat loss. So you could get bigger arms by doing pull-ups, squats and deadlifts!
Progressions are key to improvement, since if you are doing the same workout that you were doing last year and nothing has changed in the last year, it is highly unlikely that anything will change in the next year either. Our bodies can get used to fixed exercises so we need to change them from time to time to circumvent this adaptation. This change could be including new movements, changing repetition range, increasing poundage or decreasing rest periods between sets to name a few. Lastly, you should go to the gym with a purpose and a plan, which does not involve socializing or texting. Often when we spend 2 hours in the gym, it's more likely because we had long rests and wasted time rather than really lifting for 2 hours. Shoot for 1-1.5 hours at most, unless you are trying something advanced, keeping rest periods short (45-90 seconds), and you will get a kick-ass, efficient workout.
Hypertrophy Specific Training (HST) is one such workout, which captures the essence of what I outlined above. I have been doing it for last 8 months, and as the name suggests this workout is geared more towards hypertrophy (muscle gain), so if this is not your goal, you might wanna look into another program. However from personal experience, my strength improved on HST as well which always feels great. Furthermore, HST doesn't tell you to do exactly X (some programs do), but instead provides a framework allowing you to design your own plan around that. Lastly, it is only 3 days a week, an hour or so per session, making it very accessible even with a busy schedule. We can almost always take 3 hours a week out for ourself. Since I have stayed good on nutrition, this is all the exercise that I have done for last 8 months without even incorporating any cardio.
If you were to google HST you will come across quite a bit of detail, ranging from some scientific backing behind the principles of HST to involved guidelines about designing your own HST workout. To avoid much redundancy, I would try to be as concise as I can be while conveying the essentials. Enthusiasts are welcome to dive deeper into this or other workouts. HST is a full-body workout, so first step is picking a good exercise for each major muscle group (quadriceps, hamstrings, calves, chest, back, abs, biceps, triceps, shoulders). The basic ideology is to train in different repetition ranges (15, 10, 5 and maybe even 3). Before starting the program, you need to figure out your maxes for these rep ranges. This means, that for each exercise you selected, you need to find out the weight that you can only lift for a maximum of 15, 10, 5 and 3 reps. For example, if my 10 rep max (RM) for deadlifts is 245 pounds, I cannot lift that weight for another rep keeping good form, or in other words I reach positive failure at 10th repetition. To speed up this max-figuring process, there are a lot of online calculators and charts (like this), which will tell you what your x-rep max should approximately be, given your y-rep max (x,y ≤ 12).
Now that you have the numbers, the preparation is over, and it's time to get started. For the first two weeks you will train for 15 repetitions, for the next two 10, then next two 5, and lastly if you are feeling adventurous 3, leading to a eight week cycle, after which you are supposed to take a week or two off from heavy lifting. During the break you can still do some lifting, running, dancing, acrobatics or whatever floats your boat. This rest is important to avoid muscle adaptation, and it is called strategic deconditioning. Lets concentrate on each mini two week cycle now. The idea is to start lower than your max, and build up to your maximum for that repetition range in two weeks (i.e. six workouts). Taking up the example of deadlifts for which my 10 rep max is 245 lbs, I would follow this progression of deadlifts for my 10-rep mini cycle: 145 -> 165 -> 185 -> 205 -> 225 -> 245. In general, I go for ~10% of reduction from my max for each workout. I do have some other tweaks that I use now, but those are finer details that can be discussed separately.
Here are the workouts I chose for my last HST cycle (I am now on my 5th cycle):
Exercise (15 RM, 10 RM, 5 RM, increment)
Leg Press (240, 260, 280, 290, 20)
Deadlifts (225, 245, 265, 275, 20)
Hammer Seated Inclined (140, 165, 185, 190, 10)
Pec Flys (120, 135, 150, 155, 10)
Machine Rows (55, 70, 85, 90, 5)
Seated Rear Deltoid rows (85, 105, 125, 5)
Barbell Curls (60, 70, 80, 90, 5)
Triceps V-bar Pulldown (50, 57.5, 65, 67.5, 5)
Seated Calf Raises (80, 90, 100, 105, 5)
Machine Crunches (125, 140, 150, 155, 10)
I will change my workout strategy again, possibly after one more cycle of HST, because although I like it, I do wanna challenge myself in different ways. There are a lot of interesting and established workout philosophies that one can try (google or bodybuilding.com are your friends). I am thinking about training for flexibility next to further reduce my chances of injury, and being agile also feels good from personal experience (I have done some dance, tai chi, etc.).
I have heard a lot of people complain that working out in the gym is boring, and I sincerely feel that you can make it as exciting as you would like to. Just like any other sport, you get only as much out of it, as you put into it. Heck, even for video games if I can't unlock any achievement or conquer a new hurdle I would find myself bored. So, unlock new achievements, like lifting heavier, improving your form, reinforcing the muscle-mind connection, making workouts more intense and efficient, and so on. If you keep on doing the same thing without any plan or a prospect of change, the gym can't be blamed for being boring.