Leveling When leveling you can take two different paths, one standard and one which gives lower exp but higher drop rates.
While the higher drop rate route does not provide as much farm as the farming specific maps, its a good alternative if you wish to earn as you level up and do not mind the lower exp gains. If not you can stick to the standard route which will get you level 300 faster.

It is worth noting at this point it is ALWAYS worthwhile killing and hunting giants they drop around 10 times more penya then the smaller mobs of there kinda as well as silver keys and when i get around to it will also drop monster hunter tokens.
Ciminal Island: This Map provides increased EXP compared to normal Leveling mobs and can be accessed via a ticket purchased with IP/VP from the item mall.

Mobs start at level 215-300 and the map contains a few useful NPC's as well as a permanently stationed GM Buff Pang
Quests: The Insanity Treasure Box Of Quests NPC located in all towns may give you a static % towards your next level regardless of your current level, at last count there is about 11 levels worth of quest rewards.

Level Up Rewards: As you level up you will gain the following rewards:-
       *Level 50- Scroll of Amplification ES (S)4 x3
       *Level 100- Refresher Hold x2 + Vital Drink X x2
       *Level 125- Remantis Laccotte (small) x300
       *Level 150- Insanity Exp Potion 150% x1 + Insanity Exp Potion 300% x1
       *Level 175- Remantis Laccotte x300
       *Level 200- Red Chips x100 + Common Treasure Chest and Golden Key x1
       *Level 210- Red Chips x150
       *Level 220- Red Chips x200
       *Level 225- Rusty Treasure Chest and Golden Key x1
       *Level 230- Red Chips x250
       *Level 240- Red Chips x300
       *Level 250- Red Chips x350 + Old Treasure Chest and Golden Key x1
       *Level 260- Red Chips x400
       *Level 270- Red Chips x450
       *Level 275- Rare Treasure Chest and Golden Key x1
       *Level 280- Red Chips x500
       *Level 290- Red Chips x550
       *Level 300- Red Chips x1000 + Ancient Treasure Chest and Golden Key x1

This is just a basic guide section, for more in depth leveling guides a few have been done by players:-
Level 300 in 3 hours by Alerassus
The quickest road to 300 by Sport
Leveling Guide Forum Section