Strength and conditioning training used to be the domain of secretive experts. Overheard whispers in the back of gyms about Russian ballistic training mingled with Texas barbell magic and was brewed together by the cabal of fitness gurus and drip fed to the public in the form of magazine articles.
Those days are fading and research driven solutions that have been tried and tested in the weight rooms and sports fields all over the world are now published and available for all to see.
The following is largely taken from Haff's (2012) excellent chapter "Resistance Program Design" in the National Strength and Conditioning Association's evidenced based manual: The Essentials of Personal Training.
These four pillars prop up and support any good program that a personal trainer or anyone else might lay down for you. I would also consider the order to be important. The first pillar is the most important part in designing your program, with the fourth one being somewhat less so.
So here they are:
Respect the Pillars, they prop up everything else in your program!
This is the most important part of program design. You should not just be doing random exercises or copying the program or approach of other athletes in other sports. You should be focussed on achieving a clear set of goals that are specific to your own sport/interests. Or as Haff (2012) puts it:
"Training programs/workouts with a specific goal in mind based on each client’s individual needs"
This can be accomplished by targeting specific muscle groups (I need stronger legs for my sport of basketball so I should squat), energy systems (I need to sprint for my sport so I need to anaerobic conditioning), speed of movement (I need to move fast and change direction for my sport of football so I should do speed drills), movement patterns (my sport of strongman contains an overhead press so I should drill pressing movements), and/or muscle action types (I need to get bigger to be a better rugby player so I should do bodybuilder style hypertrophy training).
As you can see off the shelf cookie cutter approaches to training (Just squat, bench and deadlift and you will be fine) are out and a more nuanced and personal approach is better supported by the evidence.
You should be making progress in the gym. After you have agreed on a plan and exercise/workout selection that meets your specific goals, the next step is to makes sure that the exercises are getting harder each time you do them. This doesn't just simply mean adding weight each time. There are a number of methods that can be used for example:
Increasing the load: This is adding more weight, like adding 2.5 kg to a barbell bench each time you do a workout
Increasing the volume: You could add more sets &/or reps to the same exercise like adding an extra set of kettlebell swings each workout until you can easily do 5 * 30 secs
Decreasing the rest periods: This could be done in a conditioning workout where a trainee does high effort cycles for a fixed period at fixed resistance and RPM and then rests a fixed time. As endurance improves the fixed rest can be reduced over time.
Increasing the velocity or explosiveness of the movement: Here the example could be a speed workout with the barbell. The weight is kept fixed during the training block but the client is asked to move as fast as possible. As explosive power increases bar speed increases under the same load.
The number one thing that I see that separates people that make progress in the gym from those that don't is correctly applying this overload principle. Many gym goers just oscillate around the same light to medium weight and do not have a clear system of overload in place in their training.
Progression is the big brother of overload and they work together to form the fundamental training idea of progressive overload. How is progression different? Progression covers all of the more nebulous factors that surround overload. Progression covers exercise quality, so a lifter who performs the same lift during a training block but does so with better form or with less nervous system effort is still progressing even if they are not overloading an exercise. Progression also covers exercise difficulty. Many athletes could benefit from doing the Olympic movements but the mobility and technical demands of a full Olympic snatch are considerable. As such training movements should progress from the simple to the more complex. In addition progression covers things like training frequency (how often you lift) and patterning of deload and reload periods.
Again many gym goers are quite happy to just sit on the same simple machines each week. While this is easier than learning to squat properly they are not progressing their movement patterns or movement quality and so failing in this third principle.
Way down at the bottom of the pile is pillar four variation. Your body gets used to the same stimulus if you keep it the same. Even if you are progressing and overloading that movement (like you are adding weight to your squat and working on mobility and form) your progress will begin to stall out over time as your body gets used to the same stimulus. Throwing in some variation in your program (like a front squat or jumping) can often help break through these plateaus and also assist your body in understanding the movement pattern leading to further progression. Anyone who has reached the end of beginner linear program like 5 * 3 or 5 * 5 will know this feeling, the grind of trying to get under a heavy (or not that heavy!) barbell to do the same three moves each week gets you down and beats you up. Here is the correct time for exercise variation, to give your body a kick and your mind a break.
I see far too many people who focus on this last pillar too heavily. They are always running from one program to the next. They might do a Men's Health workout this week or Chris Hemsworth's Thor workout the next week etc. but in overdoing the variation they are sacrificing pillars 1-3. Get the basics right and be consistent in those before you add in more variation.