Check your chain, there is a measuring tool to check if you need to replace your chain.
Check knots & bolts, cassette & pedals (check for lose parts) make sure they are secure, creaky/squeaky sound is not good.
Check & clean bearings – if its sealed bearing I still clean the outside. If not sealed clean and grease it.
If you have tubeless, you should refill sealant regularly
Check / replace brake pads
Bleed hydraulic brakes & check the hydraulic cables for damages.
Check & tighten spokes, most of the time you don’t notice the nipples until it’s broken. Check the wheel alignment.
Brush & Floss it – clean those joints, try not to use high pressure water or air
Lube it – lubricate those joints/moving parts (not all)
So far this is what I can remember. It’s better to have someone who knows more to check/fix your bike or at least guide you. In my case I always call the experts Bern, Angelo and/or Jr.