First try contacting the FBO on unicorn.
...and if that doesn't work, try the pegasus! (love autocorrect!)
First thing I usually do is search for the airport on
www.airnav.com, to get a general feel for what's there in advance.
How many FBO's are there? (Usually only one, but some places might have more than one. Or none.) It'll list phone numbers for any FBO's.
It'll say whether their fuel is full service (FS) or self-service (SS).
An after-hours call-out for full-service fuel will usually cost you something, maybe $100 or thereabouts. There may be a sign on the (locked) FBO door with the after-hours contact number.
Most self-service kiosks are 24hours and accept credit cards. Except, of course, for the ones that aren't, or don't. Or are broken.
It's not always possible, but if you can be present while someone else fuels you up, make sure the truck says "100LL" on the side. If someone asks you if you want something called "Prist", they are confused and DO NOT LEAVE until you make sure they are going to give you 100LL and not jet fuel.
Some FBO's like to marshall you in. Some don't. Look for a guy waving his or her arms at you. They may or may not be carrying orange sticks. If you don't see a waving guy, then pick a spot that looks like it's what other people are doing or have done.
At some places, transient parking is labeled. Most of the time it's not and you just have to guess.
At some places, if there are already ropes there at a tiedown spot, this is someone's way of saying "This is a rented spot that already belongs to me - don't park here."
At other places, if there are already ropes there, it means "Park here! We've got ropes!"
Parking customs and etiquette is somewhat a matter of "local culture", and there's no way to learn it in advance except to show up and ask.
(Have I ever parked somewhere, and come back to find the plane in a different place, with a note on the window saying "You took my spot and I had to move you"? Yup. Done that...)
A set of tiedown ropes and travel chocks should be standard equipment for the cargo compartment of any plane IMO.
Tie one end to the hook in the ground with something like a bowline knot. Then, for the strut-end, I use a taut-line hitch, like this one:
https://www.aopa.org/news-and-media/all-news/2017/june/flight-training-magazine/tiedowns
If someone else ties you down, inspect their work (if you're present) and make sure they've done it right.
Think of "showing up at an unfamiliar airport" as like traveling to an unfamiliar city or country... an adventure of discovery of a new culture! Don't be afraid to get it wrong and look like a newb or a tourist, it's part of the fun! Rehearse the following phrases, and use them on the locals:
"Is this an OK place to park?"
"Can you help me work this fuel kiosk?"
"Ground, can you give me a Progressive to the <parking/fuel/restaurant>?"
"So, what's cool to do around here?"