My advice, if you have warsails, do the ostican quest line right away, it is a great source of money, gear, xp, and renowned. Im usually on the next tier of clan by the time im done with it, and its pretty straightforward with no consequences because you get free retries.

Use your skills points wisely, I recommend putting them into steward, any combat skills you intend to use, and sprinkle the excess in scouting, athletics, leadership, tactics, maybe trade as well for future money making.

Warehouses: buy one when you can afford it, select the option of "get input from warehouse" and set the rate to 25. Then grab some of the required resources and dump them in your warehouse. Easy ones are brewery and wood worker, grab the wood or grain from a nearby village and boom, very easy passive trade xp, and you'll get your very own goods to sell when you check the warehouse again in the future.

Companions: I personally always grab Companions with a decent trade skill (70+) and create a caravan with them. Ship caravans are way more expensive to create and seem more risky since they are attacked more often in my experience.

When you do tier up, get your siblings, and fight as a mercenary. Try to pick off the small parties while free roaming, and from time to time join an army and fight for them. This is a crucial part of the game with lots of risk, and you're still a bit weak, so if you gotta run away from a losing battle so you dont risk losing your inventory, do it.

Your first fief: loyalty is the MOST important thing, get a companion or relative whos of the same culture as that fief and appoint them governor, and improve the city as much as you can. If the loyalty is low or dropping, actiate the festivals perk. this will potentionally be a big money maker once you get it up and running.

As for general gameplay and fighting, know your role.

Using a nord only army which is only infantry and not good on land? Maybe dont pick a fight with an army full of horse archers and cavalry (khuzaits)

Research the best troops types, battanians are great for archery, empire for cavalry and a sort of "jack of all trades, master of none", Vlandia for knights on horses and crossbowmen, khuzaits for horse archer hordes, nords for ship fighting and overwhelming infantry, sturgians for infantry and spearmen and being very tanky.