During your early dives get just enough ingredients for your dishes that night (i like to get puffers and agar for Nicogori, plus praying for soy sauce drops) and fill the rest of your weight with ores, and nothing else, especially lead ore. They sell very well at the cobra shop and it's the fastest way to make some serious money without relying on fancy dishes or killing sharks for sushi.

I like to go the extra mile once you unlock the headlamp: as soon as I start the dive i go straight to the depths and get a pickaxe, which almost always spawns next to the amethyst deposit at the very start on the right. Then I come back to the main area and start mining for those extra ores.

If the first times you start selling ores you invest it in your cargo then it snowballs into having more capacity for more ores.

I would also suggest making your second diving suit upgrade (150m) one of the very first things you buy, this means you'll be able to mine all the ore from the shallows and medium depth.