First off, work closely with a good vet you trust.
I always did a pre-season performance exam, so the vet had eyes on the horse for a soundness exam, became familiar with his responses to flexions, etc. and we could address any issues early. I will say Rusty competed Prelim and CCI for several years before ever needing injections - I am definitely not one to inject unless the horse actually needs it. For him, that was prepping for his second CCI long format, when we did inject his hocks and coffin joints. We moved up to Prelim when he was 11, and he continued competing upper level including running Intermediate at 16.
Day-to-day, lots of hacking, especially up and down hills. Turnout as much as possible. Icing after every jump school or gallop. Pentosan every two weeks, and a Legend round once or twice a year. He also got Legend the day before cross country when he was competing. Liniment baths and epsom salt soaks in the summer after rides, and a Back on Track sheet in the winter. PEMF every 2-3 weeks, depending on how intense his schedule was at the time (this really helps his SI). I keep him on a high dose MSM feed-through joint supplement (for him, this makes a big difference and I can tell when he’s on it vs not), as well as a hoof supplement and a GI supplement. He gets UlcerRx when he travels. Alfalfa hay, and high quality feed to help keep weight on. He stays on a regular 5-week schedule with a good farrier.
I’ve done chiro and acupuncture with him, although not on a regular schedule, just as needed. I also now have a bodyworker who does him semi-regularly, which I think is helpful and something I probably could have added sooner - I started working with her when he was coming off extended stall rest for a tendon injury and was quite tight.