If you actually want to fish, for levelling/grinding personally I think mine fishing is the way to go and get hold of a good quality pole (not rod) 60+ ql. The pole also uses basic fishing line so easier to make.
The logic behind this is that there are only 3 types of fish and only one 'big' fish, the wurmfish; whereas on surface you have pike, salmon, carp, catfish, brown trout - all likely to jump hook or snap you.
I used 62ql pole, 20ql basic line, 20 ql orange hooks (no bait) and 30 ql feathers (I asked my local farmer nicely, she keeps chickens:) )
Wait for the first splash, activate sleep bonus, double click on tile on second splash (I find this better than one click), catch fish (or lose it), turn off sleep bonus, Repeat and active sleep bonus as soon as possible.