From my experience, the trick to filling up those fish bundles when you're just starting out is getting your hands on that training rod from willy's shop for just 25 gold. It's a real game-changer since it makes the catching bar bigger, and you can focus on building up your skills with easier fish first. The mountain lake is perfect for this, especially going after carp since they're pretty chill and give decent experience.

Something that might be interesting, you can actually knock out the crab pot bundle first by just collecting stuff on the beach like clams and oysters, no fishing required. Once you're feeling more confident though grab yourself a fiberglass rod and start working through the seasons. Spring is great for sunfish in the river, and if you catch a rainy day definitely try for catfish in the secret woods. Summer you'll want to focus on red snapper and tilapia near the ocean, and fall is your time to grab tiger trout and walleye, especially during those rainy nights.

Good to know that the traveling cart that shows up on fridays and sundays sometimes sells rare fish you need, and if you're having trouble with specific catches try using some trout soup for that extra fishing boost. The nighttime fishing can be really rewarding too especially for eels, and don't forget about checking special spots like the mines or sewers for unique catches. Once you get access to ginger island that magic bait becomes super helpful since you can catch any fish regardless of season, but honestly taking it step by step and focusing on the easier catches first is the way to go. Fish ponds are pretty handy too since some bundles need specific types of roe and they give you some passive experience while you're working on other things.