Id recommend having some drone defense at minimum on your CV and make sure youre not too close to enemy bases, use a scanner to see whats around you

Going up to the Sun sector is typically the safest. Go to space, point your ship in the direction of the local sun and a warp lock will come up orange. You can fly towards it and press K to warp to the sun. Otherwise if you absolutely have to park it on a planet and you're unsure if there are any hostiles around, park it at the poles. There are clear marking on the north/south poles of the planet that prevents hostile from spawning in it and patrol ships will not patrol into it. However it does cause some issues too. Like if it's a heavy 4G planet and you can't take off, and want to try to add thrusters to your ship, it won't let you do any modifications to your ship because you're at the pole. Alternatively in space sectors, if you see poor quality asteroid belts, warp in point is generally pretty safe. In fact pretty much all asteroid belts warp in point are usually pretty safe. Exploration sites, hack sites, UCH, Mining sites, trade sectors (non hostile) are good too.

When I'm exploring a system, I park my carrier just beyond the boundary of a low-g planet or moon's pole, not so far into it that it starts doing weird spinny things. So far as I've seen, no NPC ships can enter or "see into" the polar area of a planet, so even if a patrol vessel flies close by, it won't attack. My carrier uses no fuel when its thrusters are turned off but everything else, including shields and weapons and a constructor or two, is running, so I leave shields/weapons on. However, my carrier has never been attacked when parked on a pole, so I could probably turn those off if I needed to, to conserve fuel.

I have a small, more easily land-able, warpless, high-G-capable CV (which begins life as my starter CV with a warp drive) with a large cargo capacity that I use to fly around the planet to scout it and, in combination with a combat SV that it can carry, use to take out and loot any POIs I want to attack. It also uses no fuel when the thrusters are turned off but everything else is on, so it can defend itself for a short time if necessary. I have a high-G-capable mining SV that has a jump drive, so I can use it to scout around the other planets/moons/sites/asteroid fields in the system and mine anything in it that I want, be it asteroids or deposits on planets. If there's anything on a different planet/moon in the system that I need other ships to deal with, I move the carrier to that planet/sector.

Once I've done everything I want to do in a system, I pack everything pack to the carrier, then fly off to the next system. I don't build bases, aside from a shelter at the very beginning and a temporary "pocket furnace" that I use to smelt any ore that constructors can't smelt, so my carrier is my "base."

You can also just turn off you ship once you land and generally no enemy will attack your ship because it won't register as a threat if it's off. Be sure to shut off oxygen first which will suck the oxygen currently in your ship back into the O2 tanks so you don't lose it, though you might get the venting message anyway when you press 'Y' to shut the ship off, but the oxygen won't vent if you've turned it off in the 'P' menu first (two things to keep in mind when shutting off a CV. 1, if you have a garden your plants might die, and 2, if you have stuff in your fridge that might spoil if you're out of your ship for very long). So if you have a fridge or two with items that might spoil, and or a garden with plants you should try the other suggestions given in here.

Admittedly I rarely use carriers, but when I do I usually just park it where I come out of warp, unless there is already a POI or OPV in render distance. A playfield has to be loaded in order for an attack to occur; why you don't come home to destroyed planetary bases when you get home, but will experience an attack shortly after.

If there is an OPV that could potentially render in range of my carrier as I return, I simply make that my first target before going to any planets, stations or asteroids.

Some star systems have locations, you can warp to, that just say "Empty Space" and there is nothing there. I have found these safe to build bases in.