A rather sizable chunk of musculoskeletal issues can be improved by improving your posture and your step. But, if you're like a lot of people, you never really learned the right ways to stand or walk for optimal health -- you've just been walking as you've always walked, choosing shoes mainly for style, comfort, and price rather than whether the arch support was correct. This combined with poor-quality shoes, a lack of stretching, and other factors can lead to foot, leg, and back problems. Wearing orthotics that help cushion and support your feet, as well as modifying your walking style, can help solve those problems. But, you need to know what you're dealing with.
Commercial Slip-in Insoles
In many cases, such as when people end up with conditions like shin splints, commercial slip-in insoles are often the first line of defense. These are readily available at stores and easy to modify (many contain printed outlines that you trim along to fit the insole to your foot size).
They can also move around and slip forward or back as you walk, and some types can begin to shred as they get older. You may want to try a couple of different types, such as foam versus gel, to ensure you find the insoles that work best given how much you walk.
Full Custom Orthotics
Sometimes the store-bought stuff isn't fine, and you need custom-made orthotics that cradle your feet. These cost more, of course, but they often last a very long time and are made specifically for your feet and all their curves and bumps.
These orthotics do wear down with use and time, as you'd expect, but they can take much longer to do so compared to a store-bought foam pad. If store-bought orthotics aren't helping you, seeing a podiatrist for custom orthotics is your next step.
Partial Inserts and Supports
When you're at the store looking at those insoles, you'll see additional types like heel inserts, cushions for the ball, and sides of your feet, and so on. These are not going to be custom fits, obviously.
You can use these for minor issues like chafing shoes, but don't combine them with custom orthotics. If you have issues with custom inserts, go back to your podiatrist to have the fit re-evaluated.
Which type of orthotics will work for you depends on your health and the cause of the condition you're dealing with. If you are not having luck with over-the-counter inserts, see about custom orthotics for steadier relief.