>>2104599
Do NOT play on prestige 20 right from the get go. I started on prestige 6 and only increased it when distance from the citadel forced me to. The earliest settlements are the roughest because you have next to no starting supplies (no building materials is especially painful). You could attempt to buy stuff from traders, but you only start with a single trading partner so trade routes are pretty much useless for your first couple settlements.
Plan your overworld journey in advance, your goal is to hit as many negative modifiers as possible. You will need to spend most of the resupplies on seal fragments or you won't have enough by the end, unless you play every single mission prestige 20 (which I wouldn't recommend).
No upgrades means impatience grows over 50% faster compared to a fully upgraded citadel. Unlike regular Prestige 20 impatience is a very real threat. Don't be afraid of using a human firekeeper if that bar starts getting out of hand (it's basically the only time the human firekeeper bonus is useful). Avoid Sparkdew Crystals.
Don't be afraid to use the forsaken altar. Not every perk is worth paying for but some of them can easily turn failing settlements completely around all by themselves. You can usually spare some food stockpiles since your citadel upgrades are often bottlenecked by mechanisms and artifacts, just don't go overboard.
A firm handshake will get you far.
I found that in general the best citadel upgrades are, in loose order of importance:
>free starting planks/bricks/fabric (NOT the ones you spend embarkation points on but those aren't awful either)
>blueprint pool increase
>embarkation points
>field kitchen
>training gear delivery line (guaranteed cache openers regardless of biome)
>blueprint rerolls
>upgrades that increase double yields

Beyond that, ultimately the best help is just having good game knowledge and knowing what your options are at any given time.