The word "grinding" gets such a bad wrap in the world of action role-playing games, or video games in general. It usually connotes a need for lots of time and energy invested in getting a character from scratch to a functioning state wherein good Path of Exile items can be worn and more enemies can be smashed. The thing is that the process of leveling up is an inherent part of the whole experience, and it need not feel tedious at all. What players really need to make it good across the board is to maximize reward while keeping tedium to a minimum.
Where to Grind
One of the biggest problems for a lot of players is not being able to get enough experience points in a limited time frame, which limits their enjoyment of the game. This is true for any action role-playing game, but Path of Exile does have some ideal locations for those who want to get more out of their gameplay. Here are the best locations to farm experience and level up for each act in the game.
As with any farming area, you can clear everything then reset the instance to do it all over again; this is the primary way to farm in this game.
Act I: The Ledge
This is most likely the best area to level in the game as it is simple and straightforward. Skeletons and other slow-moving monsters inhabit this location, and they're easy to clump up and clear out with splash and AoE damage. If you wish to go back to town, you can use the waypoint in the middle of the area so you don't have to use Portal Scrolls. It's a very convenient farming area for those who are in the lower levels.
There are also a few things that are interesting about this area. For instance, the pointed tip that you see on the waypoint always points towards Rocky Climb, which is the next area, so you should know where to go if you have to go there next. The Ledge itself is best for runs from end to end to get experience quickly and efficiently.
Act II: Fellshrine Ruins
This act has a few more choices in terms of farming areas, but Fellshrine Ruins is definitely the cream of that crop. You can just take a waypoint to Church Dungeon Level 1 and the exit to Fellshrine Ruins is just right there next to it. The monsters there are mostly skeletons and zombies that you can just take out with splash or AoE, although you'll have to be wary of Hulking Titans. Skip them if you're not strong enough to take them out yet.
Act III: The Docks
This is definitely the best area in the whole game to grind out experience at any sort of difficulty, as long as you have access to Act III. It does seem like the best grinding areas are those that have tons of skeletons and zombies to kill, as well as wide open spaces for kiting and safe spots for ranged classes to pick at monsters a distance.
While it's the best grinding area, it's not the most optimal one. You need to have a progression in Act III, especially if you're playing in Merciless difficulty. You can start from City of Sarn to Catacombs to Library to Lunaris. If you're still at the lower levels, you can still farm in Act I and II before you go on to Act III.