How can I prevent achilles tendonitis?

Strength training and massaging are the only things that work. Had most treatments done on my achilles after missing most of last track season and they’re the only things that made a difference for me, and now able to start XC (here in the UK).
Hit the gym: weighted single-leg calf raises and drops off a block working up to 1.5x body weight (use Smith machine for the heavier weights). Do it off a stair at home if you can’t get in the gym (currently doing this atm).
Also massage it whenever you can - tendons have awful blood supply so massage gently using one of those stone/metal massage tool things and try to get the tendon to flush red. Better blood supply helps repair any damage.

Collagen supplementation is something else to consider. In any event, if you eat chicken, don’t skip the skin.

when you run, think about pushing from the heels rather than forefoot. "strike" whatever way is normal to you but push from the heel and leave your heel pushing a little longer than feels normal.

Something I've found to be true is that certain types of surfaces can exacerbate achilles-tendon problems. I grew up near the ocean and running on very soft sand seemed to make things worse. Also, changing radically the amount of heel to toe drop in your running shoes can cause problems. Let's say you were in an old school pair of shoes for most workouts with a significant 12mm or 13mm drop and then you ran in racing flats or other shoes with essentially no drop. When I did have achilles problems though icing them in the evening and stretching carefully before workouts generally resolved the problem

Amputating your feet above the Achilles will guarantee to prevent tendonitis. 100%

Great advice. I just showed this to my kid who started running.

No problem - hope it helps. It can be such a tough injury to get rid of if it’s left too long. I’ve known guys have stress fractures that’ve healed a lot faster, so absolutely no short-term fix. In the meantime though, it’s incredible how much fitness you’ll keep (might even improve) if you throw yourself into the cross training. It’s unbelievably tedious, but sessions and easy days on bike/elliptical can be so beneficial if you can bear them. Good luck!

Man it came back because I ran in messed up shoes

My school is poor and doesn't have a very good gym. I'm back on the bike but I hope to be off soon. I'll most likely get a good month and a half before track season if it goes like last winter so I'll have plenty of time to get back in shape (and strength train)

Work on calf, feet, and ankle mobility.

kneel, put a foam roller on your calves and sit back on it. Then move it around so all of your calves get compressed.

roll your feet over a tennis ball to loosen up the foot muscles.

the goal is to get the muscles and tendons around the Achilles mobile so the Achilles doesn’t take the load.

Don't increase mileage or intensity too abruptly.

If you are eating properly and not overtraining, there is no better an option than to pray to Achilles, son of the Nereid Thetis and Peleus, king of Phthia.

Foot flexibility sounds dumb, right? I started doing some yoga stretches and it has made a big difference. Check "Breathe and Flow" on youtube. Flo posts some helpful content.

One of the reasons that Achilles injuries linger is that when you’re not running, you are still stressing by walking. To take the pressure off, tape up as follows. Anchor under your heel any good strong stretch material and point your foot down and 2nd anchor above the calf. By letting the stretch material absorb the stress, it will heal a lot quicker. I have even left the taping in place for the first few runs after recovery just to make sure.

Eccentric contraction. Use a step or a stair. Stand on you toes hanging your heels off the edge. Use both legs to extend and get up on your toes. Only use your effected side to lower yourself until your calf is fully extended. Do 20 or so a day, everyday, even if it hurts. If you need extra resistance grab a dumbbell to hold on the effected side. Do that and stretch your calf/achilles. This has gotten me though nasty achilles and upper hamstring tendonitis while continuing to run. Under MRI it's shown to heal the fibers in a tendon.

Google Alfredson protocol.

As others have mentioned, strength training and mobility are the correct answers.

There are no quick fixes or hacks, just effort and discipline.

I'd consult a physio to devise a strength and mobility program.

You want to be doing some exercises to strengthen your calves and glutes - eccentric and concentric reps, plus isometric holds (these are great for tendons).

You also want to loosen up that ankle joint, as, if your range of motion is poor, you can easily overload the tendon.

Also, be sensible when returning to running. Don't jump straight back into intense workouts and big volume, as it won't matter how robust you make your tendon - if you aren't correctly managing your training load, something will inevitably break down and you'll be constantly repeating this injury cycle.

Search online for the article (should be able to get it for free):

"A Proposed Return-to-Sport Program for Patients With Midportion Achilles Tendinopathy: Rationale and Implementation."

Read it , understand it and follow the exercise suggestions. Basically lots of straight knee and bent knee eccentric heal drops. If you have an insertional tendon injury, right at the bone. there is a different protocol, you will have to research and find what works for that.

I used to have problems but since I started "retro training" with walking and jogging backwards every training session all these things are gone. After my tempo I walk and jog easy up a moderately steep 400m hill, backwards. At the track I jog backwards barefoot and/or push a football sled backwards. It stretches and strengthens and stabilizes all the right muscles, and bonus is it bulletproofs knees, ankles and so forth, and improves form to a stronger upright position. I also fixed a really bad hammy pull last spring and now not a peep from what used to be a squeaky wheel all year round.