This guide is outdated in current 0.8.4 public test version as they fixed the immense amount of money you got from fish farms. You can do it in the current stable release and last beta version if you downgrade to it via steam console. But as soon as the new prices are in stable this guide is outdated.

First you need about ~300.000 Nok you can earn how you like: fishing or cargo missions.

Buy the tier 1 fishing ship, skill long line fishing and buy 4 500 Hook buckets. Use herring. Bait them all. Then look at the map and watch which fishing zone have the most amount of halibut. Buy the bluefang piercer and the Mariner's Fang knife as those give you bonus And are worth it.

Then set sail and head to the fish spot with most halibut. Switch on sonar and as soon as you are near the spot you'll see where most halibut is. Get out the 4 buckets of long line by going over the spot do a 180 and repeat. When you are done bring the long lines in, And hold your piercer and get the fish. If done set sail to the harbour or rebait the hooks and bring them out again. While on course to the harbour, Take your knife and gut them all.

In the harbour sell your fish filets at the fish market. You will have 300.000+ Nok pretty fast.

Buy the tier 1 cargo boat. You can hold 4-6 medium cargo depending if you like Tetris. :-D

I personally stick with max 4.

Look for maximum nm and 48hour jobs and do those missions. Takes longer than fishing, but I prefer this as for me this is more fun.

If you want to upgrade your ship, first are propellers to have more miles per fuel. Then the engines. You can set full power on the engines at tier 1 ships.

The second step is using fish farms. You need to travel 150km to get the second licence. If you have it: take full loans and get Dr. Phil and equip small smolt tank. Then take 20.000 smolt, buy a fishfarm where you want and head to it. Go to the control panel, and add fish. Head back to harbour, derig the smolt tank, buy 4 bags of 1000kg food bags, load them (small crane operator skill required) to dr. phil and head to the fish farm. Load all food into the fish farm and turn on engine. Then drive around until you have 300km travelled to get tier 3 ships. After 8 days go to the fish farm, sell the fish and redo this one another and maybe a third time.
Pay back the loans so you have no interest payment.

Then you have the skill and money for tier 3 ships.

Now you have the money and skill to buy tier 3 ships. Do what you like.

Some tips:
Handling: Service Boat tier 3 is a nightmare to handle. You give 30% power and merely move. You give 31% power and you do a jump forward. Back at 30% power, you just keep sprinting away. This makes docking pretty bad to handle. Cargo boat is fast but at power when turning your ships is just sliding throught the water and it takes a while the boat is on course but in my opinion the best easily to handle ship. The fishing boat is also good.

bow thruster:
Those are good. Take advantage of manual transmission gear. You can get the thrusters in one direction, stay in neutral and give some power to the engines and you turn where you are. You can get off docking sites easily while go fwd or rev turn in the direction TO the docking site turn your bow thrusters AWAY from port site and give a bit of power. Reminder: You need to center bow thrusters manually.

I have 3 diagrams for you to decide how much power to cruise at. Bottom axle is power on engines. Green line is speed, red line is fuel usage and blue line is litres/nm efficiency. Those are for tier 2 and tier 3 boats.

Now set sail and enjoy the game. :-)