What maintenance can I perform on my car to increase its performance?

I drive a V4 2009 Honda Accord and it is 6 years old. The car is slightly over 30k miles. Lately, it seems that the car is slightly sluggish. It could be me, but what types of maintenance should I look into to increase the car's longevity and performance?

Change fluids and filters. Rotate tires and make sure that they are up to correct pressure as well as balanced. Replace spark plugs and possibly wires. Clean throttle body. Check for vacuum leaks and repair. Learn how to check brakes and make sure they are 100%. Flush cooling system and make sure the proper coolant is in it - There are several different types. Check the belts and replace any that show signs of imminent failure. Check the hoses and replace any that are soft or ballooning.
BTW. It is an L-4. I don't think anyone has made a v-4 since Saab made the Sonnet back in the 1960s. It has no distributor cap or rotor. It also does not have points, king pins, a carburetor or a crank to start it with.

Good answer from "octep" but I will add: use a fuel cleaner every 3rd tank of fuel or so; the cleaner will help to keep deposits from building in the engine and fuel system

As long as you are following the manual's service intervals you should be fine(oil change, coolant change, air filter replacement. Etc). If it's feeling sluggish, it might be due to a part that is going bad.

BTW it's inline 4 cylinder, not V4.

Many people say not to use additives after doing all the maintenance. But there's a product called Seafoam to use for the oil and for the top manifold
area. It has a small insert that you put into the air duct pointing towards the fuel system. You then start your car, warm it up to operating temperature, then slowly add the Seafoam by pressing the spray top of the can.
The spray will want to make your car start to turn off. Stop spraying at that point. When the car goes normal again, spray until you finish the entire can.
YOUR car WILL smoke as you add the additive. But that it because it is cleaning all the gunk off your engine and vacuum system. Rev it up a bit after your finished until the smoke disappears.

I tried it after watching this guy named ChrisFix do it on youtube and he measured before and after pictures and was actually impressed. So was I. It helps your car get a little bit more power and actually runs better.