Well it really depends on what you want to catch. I like to fish with a super rod at the safari zone because you can somtimes catch a dratini and you may be able to catch dragonair too but im not sure.
Rainy places
In Fushia City you can get a Good Rod. Fish somewhere.
You fish for it in the town the third gymleader is with a super rod.
Fishing guide
Fish for it in the river by Fortree City using the best rod that you have.
You can't catch staryu in firered only in leafgreen or ruby or sapphire or emerald.
Rainy places
The best place to fish in Sacramento is in the Delta.
If you are catching water pokemon, go to a body of water and stay in that one place while you fish. that way, you wont waste steps and you will have unlimetted time
It's easy Treeko the wood geko Pokemon ,mudkip the mud fish Pokemon and torchick the fire chick Pokemon
In Fushia City you can get a Good Rod. Fish somewhere.
Rubios is the best place to buy a fish taco if you want to go plain and american.
in a ocean
Fish near ever grande city. (In emerald) In fire red you must get it in a trade.
You fish for it in the town the third gymleader is with a super rod.
Ontario
Yes, as long as the fish and Fire Bellied Toads are around the same size and the toads have a place were they can get out of the water if they want to.