Football shoulder pads are meant to protect players from injury and allow them to take and deliver punishing hits. The pads' design has changed somewhat over the years while the quality has increased dramatically. The art of lacing them up really hasn't changed much in the past 50 years or so.
Place the shoulder pads over the head and onto the shoulders of the player. Ensure the appropriate fit with full coverage of the shoulders and the clavicle bones. Make sure the front of the shoulder pads cover and protect the sternum or breastbone as well.
Take the underarm straps and fasten them to the front of the shoulder pads by using whichever fastening method the pads come with. In most instances, it will be either a T-hook insert or traditional belt strap and buckle. This will ensure a snug fit prior to lacing up the actual pads.
Lace up the shoulder pads in the centre as the final fitting element. This is a standard shoelace that would be tied in the same way you would tie your cleat or other lace-up type shoes. The snugness of the lacing is always based on personal preference. Some players prefer a tight fit, others want it more it more loose. This "feel"can be manipulated by adjusting the tension of the string.
Tie the laces in one of a couple of different ways. Many of today's shoulder pads come with the quick-tie feature: a small plastic slide that tightens and locks the laces in place. The quick tie is a more modern feature in sports equipment that takes the place of physically tying the laces for security. It also limits the likelihood of a lace coming undone during play.
Attach the rib protector or flak jacket as it is sometimes referred to. These also have a shoelace that will need to be tied as well.
Adjust the tightness of the pads dependent on the weather. Players will generally add more layers of clothing if the weather is cold and obviously take layers away if the weather is hot.
For youth players, buy a good set of standard quality shoulder pads. Upgrading to position specific pads is really not necessary until the college and professional levels.