It will depend on how many miles you ride in a week but waxing my chain has simplified my bike maintenance a ton. I only ride about 24km a day though, so it takes a bit to get to 300km and need to re-wax them.

I also ride my MTB in very sandy and gritty dirt, the wax sheds this off and improves the lifespan of my chain. I needed to constantly clean the cassette and chain when I was using "dry" lube. It definitely is a pain to re-wax, and it's not a perfect solution for everyone, but if the dirt you ride is sticking to your chain/cassette, it's the best I can recommend.

I would also recommend keeping your fork and/or rear suspension maintenanced professionally. I will sometimes do a 6 month service myself, but sending my fork in every 100hrs of use has kept it buttery smooth. Some shops will help get you the optimal performance for your body weight and riding style too, you'd be surprised how much speed can be gained with a tune.

Other than that, blead brakes if they're hydraulic, check tires and sealant, and if you run carbon parts it's always a good idea to check for cracks or rock strikes. Carbon is strong until it isn't, and no one wants to end a race because of a broken part.

Sorry for the long ass comment, hope this at least helps