Almost 33 here and I believe we can still progress physically at this point. Lets assume you have a limited number of hours per week for all physical activities (less than 7 hours per week maybe?) and that you need to train your endurance as well as power/strength and of course your skateboarding skills.
1. Dynamic stretching for warmup.
2. You probably have a smaller bag of trick but make it consistent. If you do, combos will provide you with enough variety for skateboarding to feel fun for many more years.
3. For me, trying to skate like Tiago is my goal. Proper speed, a bit tech but no circusy, equal amount of switch, and trying to pop as high as I can. It just feels good to have explosive power when you get older. No jumping down shit and progress like PROD - little steps, no unnecessary risks. Tranny skating is reserved for 40+.
4. Avoid injury at all costs - rebounding after a proper injury will take a lot of time and rehab will be even longer.
5. After your body starts to feel drained at the end of the session, stop with hard tricks or skateboarding all together. To grow muscle etc. continue with jump rope or sprints, box jumps etc. until you can't even (training until failure). Eat some protein after.
6. Static stretching after? Haven't come this far yet, but probably should.
Skateboarding can also be a crazy cardio workout - find a big flatground lot and do as many (simple) tricks in quick succession, either over (smallish) obstacles or just on flat. Then do sets of those and you will improve your endurance and your skateboarding skills. You will feel the burn for sure and HR will spike.