I need to start catching up on the MLP comics sometime. Any recommendations on where to dive in?
You can really start with any volume. There are three different series, one of which ended. The main series has arcs, while the other two are all standalone mostly slice-of-life stories.
Main series
Volume 1 - Return of Chrysalis arc, really good besides a weak resolution
Volume 2 - Nightmare Rarity arc, a bit repetitive and I didn't think Nightmare Rarity worked that well as a villain, but a lot of people liked this arc, I thought it was fine, and I liked the resolution
Volume 3 - two arcs, one about Big Mac trying to find some nails to buy during a festival, and one about how Cadance and Shining Armor met, which are both fun comedy arcs
Volume 4 - also two arcs, the first being the first one to use Princess Twilight; one about the girls joining a pirate on his quest, which I liked a lot but others don't seem as keen on, and another about a magical bookworm causing stories to come to life, which had some good parts but was surprisingly dull, I though
Volume 5 - yet to be released, but is about the newest arc about Celestia's past and an alternate reality, which started with two really good issues but then proceeded to have a disappointing last two issues, but is still a decent enough arc overall
There is also the Micro-Series, which is collected into two volumes called Pony Tales. Each of the ten issues is standalone. Twilight's issue is thought to have bad art, and Rainbow's issue is thought to have bad dialogue, but otherwise they're all fine.
And then there's Friends Forever, which should only have one volume out now. Like the Micro-Series, the issues are standalone. The first one is considered bad for multiple reasons, but otherwise they are fine.