Really depends on how much riding you do and the components on the bike. Back when I was younger and more fit and riding 100+ miles a week I did a lot of maintenance. Some of it was necessary like adjusting brake pads, cables that developed slack, etc. Some of it probably wasn't but gave me an excuse to tinker.

Now I'm riding less, I find I don't need to do as much except keep the chain clean and tires inflated. I still check cables, chain slack, and stuff but they tend to need less work now.

You're probably fine with your annual tune up. If you want to do it yourself the drive train should be your highest priority in my opinion:

- Keep your chain clean. Every few weeks use a degreaser to clean it, wash it out with water and apply lubricant suitable to your weather conditions afterwards. There's a chain cleaning tool from Park Tools which makes the degreasing part particularly easy. I highly recommend it.

- Replace the chain every year. Chains will stretch and wear out the cogs on your cassette thereby deteriorating the whole drive train. There are distance recommendations and ways to mesure if it's time to replace the chain if you want to look them up, but doing it every year shoudl be on the safe side

- Replace your tires once they are worn out. I drive Continental Grand prix which come with a handy indicator on the tire itself, but you should be able to look up the recommended life span for your particular tyre

- Keep your bike clean. Cleaning your chain should be a welcome opportunity to also quickly clean the rest of your bike - doesn't have to take longer than a few minutes.

If you are going to a bike shop once a year for maintenance, then you are doing the maintenance you should be doing.

But many people have old bikes with rusty brakes, non-working gearing, and just go on using them until they fall apart.

Also, different bikes require different levels of maintenance. And your riding style and frequency of use affects the speed of wear.

Once a year is plenty unless you're having unexpected failures or a poor experience. If you're riding enough to go through parts faster than that, you'd know it.

If you commute by bicycle every day rain or shine, then changing the cables twice a year might not be as crazy as it sounds. I doubt that's enough time for them to rust to the point of being in danger of breaking, but it probably is enough time for them to collect enough grit to interfere with smooth shifting and braking. Though a lot of that will depend on how exposed the cables are on your particular bike.