You know those days at school or work when you forget why you're there, and it just becomes a string of meaningless tasks? That's grinding. As long as the player has a goal that's bigger than the grind, they won't see it as a grind.
The trick is to keep the player fueled with new challenges so they never feel they've gotten stuck in the grind. (I remember times in WoW when I seriously considered smashing my keyboard with my face
while grinding on trogs for an item drop.) Good challenges for the player might be learning tactics against a new enemy, exploring a new area, solving a dungeon, or nabbing quest items. In Nurica, I make a list of all the cool challenge/quests that we can do, and then space them out in the gameplay so that there's always something interesting to do.
Players also need goals that give purpose to their grind. It's sort of like their reason for playing the game. Typical goals might be an item/skill they want to earn, a status they want to achieve, or a storyline they want to unlock. Then at the end of each goal is a reward.
Another idea to spruce up the gameplay is to add an achievement system. Players like to be rewarded, and nothing breaks up a grind like finding out you accidentally unlocked a prize by killing 20 monsters without getting hit.