Build an accounting room on your flagship as soon as possible (unlocked after having 100k gold for the first time).
You get 2% extra profits per calculating level that your assigned character has, which might not seem much at first, but it adds up fast, if you get 10% or more extra gold per sale.
You also only need to have the character in the accounting room, when you actually sell goods, so they can be in a different room during voyages.
I’m using Lu Liyuan (joins if you start with Yun Mu, idk if other starters can get him as well) as accountant and surveyor, for example.
Another room you want built as soon as possible is the studio (unlocked by having knowledge of 50 types of goods), which has a 3% x your characters selection skill lvl each day to turn one of the goods on board of your ship into premium goods.
This not only makes them more expensive to sell, but they are also needed for several trade quests, so it’s good to get that room as soon as possible.
You do need to have one character in the room for the entire time, while you are at see though, so they can only have that job and possibly a combat related one, if you’re willing to switch them around for combat.
Use triple forward shrapnel cannons + 2 heavy metal armor + large ship of your choice.
Given the setup above, you can solo every single bounty. Leave the rest of your ships at a nearby dock to minimize losses.
Avoid bounties in narrow areas (Persian Gulf, Florida Straits) since pirates always have high positional advantage on contact.
It is very possible, even easy, to find routes early on that allow you to grind up money reliably over time. It is tempting, then, to do exactly that, only exploring once you have plenty of cash under your belt.
Resist this urge. Exploration offers rich rewards, both monetary and otherwise. In particular, the more you explore the faster you can find new crew members, who’ll serve vital roles to empower your ship. As well, the further you explore the more likely you are to find even more lucrative trade opportunities than that available in your immediate area. That’s not to say that a little grinding now and then isn’t out of place if there’s some specific thing you want to save up for and it’s within relatively easy reach, but try not to burn yourself out running back and forth endlessly between two ports when there’s so much more to do that gives you so much more.
Also, on that note, when you get new crew members try to level them up somewhat when you get a chance. Not only does this unlock various bonuses, it frequently unlocks various sidequests.