The 2 factors that affect drops are luck and drop-rate, it is important to improve your drop rate as this can lead to more blue and gold chests, gems, money, ect. you'll want to aim for about 45-50 on your standard fighting gear (until you are satisfied with the gear you have for the rest of the game, in that case, don't bother with it at all). Its always nice to have as much as you can get on an alternate set of gear (preferably light weight gear) so that you can farm slimes for gems and stat/skill books (even holy gems can drop off of lvl 1 slimes).

Always remember, it's the amount of enemies, speed at which you kill and the level(lvl) that are the most important for picking a farm spot, you'll want to try to stay clear of enemies that move around a lot (although at some points you don't have much of a choice).

Plain Arcuz - Lvl 1 to Low 10s: Dead-end straight north of the entrance to South Mountain.
Gino Mountains - Lvl 5 to Low 10s: Go south, west, south from the Rose Forest entrance to find a dead-end filled with lvl 3 wolves and lvl 5 slimes.

South Mountain - Level 7 to 11: Go north from the Silent Hills entrance to find 6x level 9 hornets. If you ignore the slimes, you can jump-slash the hornets and take no damage.
Gino Mountains - Low 10s: There's a cave located in the Northeast corner. Several blocks in the cave have a bunch of lvl 7/9 wolves and lvl 11 slimes.
North Forest - 10 to 15: There's a dead-end east, north, east of the entrance that has several lvl 11 hornets, and one lvl 17 hornet. As with South Mountain, stay off the ground with jump-slashes to avoid being hit.
Goethe Grass - 15 to 19: Two east, one north of the entrance. This block has many lvl 17 hornets.
Guilty Forest - Upper 10s to Low 20s: The dead-end quest block.
Rest Valley - Mid - Upper 20s: Northeastern corner, and the block below it.
Rest Valley(Final) - 30+: The whole thing. Lots of enemies on every block.

If you get to the point where you are making a substantial amount of money, TP scrolls are your best option for fast looting so you can stay where the monsters are heavy, remember to check Susan's store every time you are in town, as she may have a useful gem in stock.