What to worry about if i leave my car for a year?

Okay so i had to store my car a year ago and i wasn't able to start it during this time due to where it was stored. I'm wondering what issues i may run into when i start it again (in 31 days) and maybe some resolutions to problems that may arise. Anything to do once i get it started? My car is a 2014 honda civil ex with no issues when stored. I stored it with a dust cover and a device underneath that prevents rats for coming near it to chew wires. It was also stored with a full tank of gas.

It won't just "start up" the battery has long since died. The aged fuel will be near the end of it's life but should still run. The tires will be low or flat.

Year old gas is probably still okay. It would have been better if you'd have added some sort of fuel stabilizer to it when you stored it, but I've had cars sitting for more than a year that start and run just fine on year-old gas and the fact that you stored it with the tank full instead of empty was a good idea too. I wouldn't worry too much about the gas unless it sat somewhere extremely hot for much of the year-off.

As cars sit for extended periods, seals and gaskets can dry out and leak upon using the car regularly again. On a car as new as yours though, and given the fact that it "only" sat a year, you may be okay there too. If you do notice any leaks, get them fixed promptly because they definitely won't get better with more use but I wouldn't worry too much about that on such a new car.

Your tires are probably flat-spotted to some degree from sitting in one place that long too. They may even out with some use or they may require replacement, it's hard to say for sure here. Whether they even out or not usually just depends on the individual tire more than anything else. If you notice a lumpy ride after a few days of use, you probably want to get the tires replaced.

If you left the battery connected it will almost certainly be dead by now. You may be able to jump-start the car and charge the battery that way, but once a car battery is totally dead and dead for an extended period of time it rarely "comes back" fully even after a good charging. You might end up needing to replace the battery if it won't hold a charge for long upon using the car again but trial and error might be the best way to find out.

Other than that, it'll probably be just fine. A year may seem like a long time to let a car sit if you've never let a car sit before but I've had several cars I've let sit for years between uses for various reasons and the battery was usually the only real problem I had with them (before I got smart and just removed the battery before storing the car…) when put back into regular service.

Check fluids.
Jump start it.
Check the tires.

Drive. Brakes may be a little funky/corroded, just take your time and they should sort themselves out as the pads/shoes eat through the rust.

I also will stomp on the brakes as hard as possible to see if I can pop a brake line/hose as I'd rather do it in the garage/storage than on the road.

Charge the battery. Check the fluids. Try to start. If it starts, air up the tires and drive around for an hour and get an oil change. No start, call for a tow.

Expect it to need a jumpstart, otherwise any other problem may not materialize.