What you learn while young you practice in the older age. When it comes to power lifting, the skills and techniques help you through your whole career. A large solid foundation helps in many things.

What's first ?

The first priority is technique. It has effect on everything you do. You don't have to be exceptionally talented to add 200 pounds to your total in one year as junior. In most cases, if you just do your training, the poundage's increase. The training systems does not count that much for beginner. The basic template carries a long way.
At first technique may not seem that important. But when the weights get heavier the bar starts to beat you up. Problems may occur immediately or weeks or even years afterwards. Many times careers end to injuries but what leads to those ?
Squats with wrong technique can destroy your knees quite soon. Deads done using round lower back are usual. Benches with wrong groove bugging front delts. The list is endless.
There is no excuse for lack of practice. Technique is no exception on this rule. It took months of practicing in front of mirror from lifters like 9 time World Champ Jarmo Virtanen. Why would anybody imagine technique is just up to a few tricks ? In the early 90´s several Russian coaches spent time in the warm up room copying his technique specially in the deadlift.
The best ways to train technique are to do it first in training session or train it separately. Start with small weight and get the lifts in the right groove. An empty bar is many a good tool for beginner, sometimes even less. After that move up to the weight you can maintain correct form, no heavier.
Two kinds of weight can be used. Pick up very light weight which don't stress the body, something like 15-25% of max. This is good for extra workouts. The second range is 50-75% when perfect form starts to take efforts. But the weight is low enough to keep high volume.
We all want to lift big and break records. Picture perfect technique has advantages no other thing can give you. You can bring out your strong points and minimize your weak from each lift. With the same strength levels more weight is lifted.
When training technique and form, break the lift into small parts. Let's take the squat for example. First part would be unracking the bar and the last reracking it. If you have to back from racks it would be the second part, them inhaling air and so on. This kind of practicing enables also a good mental concentration.

The training zone

Many juniors wonder why there is no progress no matter how hard they work out. This is just the reason why most stall. Too much HIT or heavy duty or other bodybuilding nonsense. The only thing gained by these methods are overtraining and bad form or even injuries in the worst case.
The best weights for young athletes are sub maximal. Most training should be done with 65-85% of max. Any more will effect negatively or the nervous system. Bad form and regression follow fast. One thing to keep in mind is that these kids make progress fast, real fast. Test the lifts often enough to keep in track of condition and monitor form in al out lifts. Do a meet or take max in the gym in every 10-12 weeks.

Reps and sets guidelines

Many youngsters waste efforts on one or two all out sets. These can be done but only in the end of the workout. Squeezing out 2-3 extra reps has no transfer on max single. It only make you more sore.
In the main lifts sets with more than five reps are not necessary. The lead to hypertrophy which can be gained by doing the right assistance work. Many times to many reps in set only lead to soreness, bad form and injuries.
Let's say you have a 550 pound max in the squat. You train with 440 and bust your ass while getting 6 or even 8 reps. Sometimes you do another set for 4-6 more reps to convince you're not done. That's 10-14 reps totally and I bet 4-6 of them are done with bad form and are most likely high. Try doing 4x4 , 5x3 or 8x2 using the same 80% or 440 pounds. You get higher volume with no reps for waste. Which option may benefit more in the meet ?

Complex is good

In the young age is good to train all kinds of stuff. Even it don't seem to add the weight in the bar it can beneficial in the long run. Concentrating on the main three in the beginning of career may lead to fast progress. Many times the only result is fast stop. A dead end is not you aim at. Be patient, most lifters have had an advantage of their athletic background in another sport. A kid in his teens doing only bench press training sounds bad to me. Specializing that don't look like injury free long career.
There are many ways to develop motor pathways and techniques. Track and field, martial arts and many other sports are beneficial for the beginner to built work capacity, connective tissues and cardiovascular system. Something that is a lot harder to achieve after packing 100 pounds of muscle mass.
However, it is another important issue when to give those activities up. When they don't enable you to train more that time has come. Prioritizing must be made at some point. Lifters must pay attention to what level he keeps his other sport activities so that they don't stall the progress in the thing. You will come to a point when it is time to change those things to extra workouts to get more work capacity and aid recovery.

The right variety

Today you meet kids who can't even stand on one foot. Or try teaching correct squat technique to lifter who has done only leg press and leg extensions. Switching from machine to another in the gym don't do anything when it comes to lift big. More beneficial to do wide assortment of variations in each lift. Try doing benches and squats with different stances and grips. It builds technique and develops motor system. When it comes to deadlift, start with the conventional deadlift first. Free weights and multi joint exercises work for everyone.
Assistance is a must. In just a few months after got started most youngsters come to the point they lift all the weight their muscles can produce strength. The more muscles the more weight in the bar. It is typical phase in many juniors lifting career. Assistance is beneficial when it comes to building muscle mass. Therefore concentrating on right muscle groups pays off.
In the squat and deadlift, start bringing abs and lower up from the beginning. Hamstrings and glutes comes next. If your middle point gives up, it can bother you for the rest of your lifting career. Discs and vertebrae problems are hard to heal.
For the bench, train upper back and lats and triceps heavy. Add some delt and chest work and you're on the right track.

Some other guidelines

Climb the tree from bottom. Start with few basics and add stuff further on. Go from simple stuff to more demanding while your technical skills improve. When strength levels raise, more volume can be added to each workout. If your athletes seems to get bored mentally, bring in new assistance exercises.
Train less per workout but train often. Many juniors pick up routines from world class lifters. Using Anthony Clark´s bench program doesn't give you an 800 bench. Many times it doesn't add your bench at all. Juniors have a fast metabolism and muscles recover fast. But the nervous systems recovers poorly due to very little lifting background. The most important thing is it don't a lot stress in one training session.
Squat and deadlift can be trained easily 2-3 times a week. The bench even more if necessary. However, many times the added volume does not necessarily add up to bar weight at meets whether you bench twice or four times per week.
It really don't take much to get started. A basic 4 times per week plan works nicely. Add couple of technique, weak muscle group or some extra workouts and progress follows. Power lifting doesn't require big sacrifices or a lot of money but patience is a must.
Usually I see great coaches brought in conversations when they have trained a big name in the sport. In my opinion, more time and efforts should be given to young lifters in the beginning of their of their career. They, if anything needs proper coaching. They are the future of the sport.