(NOTE: I haven't done this in quite a bit, because I have so many coins, so tell me some things I should change or add)
Starting off. The first thing to do is pretty simple, and you're told to do it: Spam space until you hatch. Now, you should run around and eat food until you grow up. DON'T try to kill things, because the starter fish is weak. Look out for predators, especially crabs. You've earned your first coin. Now, what you want to do is find another fish of your species and hold Q, until you get max eggs. Wait for the timer to run out, find a good spot to lay eggs, lay them, and wait. You should remember you have to eat occasionally too. You'll have to find food and your babies will eat it, and you'll get red coins when they grow up! It's a repeating process.

I kept using Pinky and the starter fish, until I got enough coins for Bibos. Remember to NOT HAVE GANG ON until you're a decent level after growing. Turn gang on and get eggs. You should lay them in one of the holes with a rock over it at your spawn. Go to the crabs, and tell your babies to stay at a far away area so the crabs don't get them. Kill the crabs, tell the children to come over so they can eat, and repeat.

Once you've got enough coins for the cuttlefish, become the cuttlefish when you want to. The cuttlefish has two spawns: The one I refer to as the "unlucky" spawn, and the lucky spawn. I can only remember the "unlucky" spawn, where crabs usually come and kill you when you're a baby which will basically make all that grinding go down the drain. The unlucky spawn is near the shark "temple" area, so if there's crabs there, just zoom away as fast as you can when you've finished spamming space. Just.. eat a ton of stuff, go over to the area where pinkies and the starting fish spawn near the unlucky spawn, and start eating them. When you grow up, you know what to do. Lay your eggs in a safe spot, and then use your lure to lure the baby fish and starting fish/pinkies to you so you and your children can eat them. Just keep grinding for a lot of money.

I'd recommend getting a lot of coins. Around 380, maybe? Just do whatever you want. Have fun. But remember, you should stll try and get coins so you dont waste it all and all that grinding went down the drain.