So most of the achievements are quite straightforward, as this is an idle simulation at heart.

As you might be able to see, this guide isn't completely finished, but will be soon. The logo image isn't done either.

Credit to DemonRat for the map:
The background part of the image is from a mod of Europe during the year 1521, and I thought it looked really well-made, so I edited it. https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3363165813 The workshop file was unfortunately removed.

Member of the Community: Play a map or scenario from the Steam Workshop

Pretty self-explanatory, download a mod or two. If you're interested in certain fantasy worlds such as Tolkien's works or maps from other games, there's probably a one that exists for it. And there's certainly a lot of historical or alternative scenarios involving earth (or a part of earth).

Beginner Map Maker: Create and play your custom map

The Quick Way: Create a new map, throw at least 2500 pixels on it (Using 50x50 is easier as you can fill the entire thing with land). Once saved, you can go back to the main menu and play the map by hitting "randomize world". Note: Using at least 50 nations when randomizing the world will help with other achievements.
The Fun Way: You can edit others' maps and scenarios in order to create your own. Maybe there's now a big France-shaped sea located in a specific place in Western Europe. Or you could create more passages/channels through mountains and the sea.
Remember that map you may have scribbled out on a piece of notebook paper, or drew on MS Paint as a kid? Split it up into different colored/shaded countries? What if that world was alive? You'd have to re-trace it, but it's pretty satisfying seeing it come to life, imo.

Geopolitical Architect: Create and play your custom scenario

The Quick Way: Instead of hitting "randomize world" on a map, hit "create a scenario" and place nations where you feel like using the "Spawn Nations" button. Once satisfied with the amount, hit "Save Scenario" and exit out to the menu. Click on scenarios, go to the one you just made, and click play. The achievement should appear. Note: It's important to save the scenario beforehand, instead of immediately pressing play.
The Fun Way: See above for Fantasy maps. For Earth-based maps that don't have the Gulf of Gallia or other edited land, I personally like using this split-up world map and annexing sections to others to customize it. I'd also like to add that there's a lot more time periods on Earth than 1914, 1942, and modern day, so redrawing kingdom's borders from the middle ages could be interesting.

Making History: Play a simulation for over 500 years

The Quick Way: Set game to 5x speed and wait.
The Fun Way: There are action commands and God Mode for you to use.

God Complex: Command nations 1000 times

This conflicts against all the achievements underneath, so I'd recommend doing it separately.
There are guides to "play" as a singular nation, and I'd recommend you try that by issuing orders and using actions to steer the decisions it takes. I'll check if any actions/commands don't progress towards completing this achievement soon.
The Quick Way: Using the nuke button and spamming it all over the place will probably be the easiest way of doing this, as it doesn't require you to re-click the button. Thanks to Vanopulo for pointing this out!

Unbreakable Spirit: Have a nation gain independence 3 times (no actions or painting)

In God Mode, scroll down to turn off "Allow Razing". Otherwise if cities get razed (and moved across the map), they'll no longer have their old rightful owner, and a differently-named revolt will appear.

Power to the People: Have a nation get 10 simultaneous revolts (no actions or painting)

This can easily happen if a very large nation has a lot of uncored cities, and has fought in too many recent wars. The chance can be increased if you set the initial nations and cities in a randomized world to max, and letting the simulation run.

Last One Standing: Starting with 50+ nations, have 1 remaining (no actions or painting)

This achievement is self-explanatory, and all that is needed is for you to wait until one nation is left. I'd recommend using a smaller map with exactly 50 randomized nations (such as Skull Island) so it can be earned quicker.

From Rags to Riches: Starting with 50+ nations, have the smallest nation become the largest (no actions or painting)

This achievement is self-explanatory, yet difficult to naturally earn.
The Quick Way: I'm shilling the scenario I made specifically for this, have fun.
Alternative Quick Way (semi-tested): In a scenario, create 50 1-pixel nations. They're all classified as being the smallest, so the achievement will appear regardless of which one becomes the largest.

Eternal Observer: Play the game for a total of 24 hours

Pretty sure you have to be tabbed in to the game for the achievement to track any progress. Will update later if I'm wrong.

Who's That Guy?: JokuPelle has landed

Spoilered as this is marked as a hidden achievement.
When randomized nations spawn, they tend to combine a prefix and suffix. If a nation spawns with the prefix "Joku-" combined with the suffix "-pelle", the achievement should appear. Note: If playing in a non-randomized map where in the scenario, the cities have been named, the achievement will likely not happen as the cities' names can be the basis of forming nations.
The Quick Way: Find the biggest map you can, and Randomize World. Turn up the Number of Nations slider to 200, and then press Play. If there is no nation named Jokupelle, redo this step. I received the achievement like that.