Apart from doing PQs, PVPs or bosses:
30-40 Mushroom Kingdom
40-50 Kerning Square
50-55 Drakes/Teddies/Truckers
56-60 Trojans/White Pangs
60-65 Robos/Mateons
65-70 Zeta Greys/Plateons
70-80 Sand Rats/Scorpions
80-90 Iron Mutaes/Roids/Vikerola
90-95 Roids/MP3/Vikerola
95-100 Gallopera/MP3/Homunculus
100-105 MP3/Captain & Kru
105-110 Captain & Kru
110-120 Ludi Dungeon/LHC
120-200
LHC FOREVER AHAHAHAHAHAHAHAHAHAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
slash Zakum arms, Temple of Time, Skeles if you're really bored.