Have you bought the Training Rod? It is available from Willy for only 25G, and it makes your green bar 2-3x bigger! Hopefully that should help with the catching part.
30 throws before you get a hit? That's unusual. Try and fill the "casting bar" all the way, and face sideways if you can. Only pull the trigger after the "!". Sometimes you'll catch trash, that's OK, it still grants XP, and you can recycle it later down the line.
What season are you currently in? If it's not Winter, then try fishing at the Mountain Lake. Especially if you're casting close to the shore, you'll be hooking Carp ~50% of the time, which is the easiest fish to catch.
If it is Winter, well, then you'll have to go a bit further afield to the Secret Woods, so that you can catch the Carp there. Just watch out for the rain, because then Catfish show up, and they're really hard! Also, there is a small chance that you'll hook a Woodskip, which isn't the easiest. Even if it isn't Winter, if you can make the hike, the Secret Woods will be the best.
Other than that, I'll give you the encouragement that fishing gets a lot easier with practice and with (in-game and IRL) experience. The more fish you catch, the higher your Fishing Level will become, and your bar will get bigger.
Hope this helps, good luck!