Train skills: Wherever monsters still give them experience ("If this skill was close to being capped, what level would I have been? What mobs was I fighting then?").
Gain EXP: The whole 40 range is rife with fighting stuff out in the altepan desert - starting in eastern altepa then moving right into western altepa for beetles in the mid range, then spiders and ants in quicksand caves for the higher levels. After that it's typically on to garliage (your mileage may vary).