Beyond Wave Echo Cave: Expanding Lost Mines of Phandelver

Picture this: You've just finished Lost Mines of Phandelver. Your fresh-faced party took down The Black Spider and wants more. You want to keep the story going but all you have is the free adventure in D&D Beyond or a starter set. What now?

I enjoy doing my own worldbuilding and crafting quests, NPCs, and encounters. But doing so as a new DM or one with limited time can be a lot of work. There's plenty of published settings, adventure books, and homebrew you can find, but maybe you want to dip your toe into writing your own stuff.

My favorite way to get started with writing your own campaign — and how I got started as a DM — is to start off with a published adventure in an established setting and build on that once the final quest from the book closes.

Welcome to Phandalin, first time here?

When I was only a few months into DMing for the first time, I was thinking about DMing a second group and I wasn't sure how much time I'd have to do a campaign from scratch. I was already DMing one game and playing in another. Plus the group would be all new players so I wasn't sure if they'd even like D&D or how long our party would stick together. So I ran Lost Mines of Phandelver so I could get started right away. By the end of the campaign I had a lot more experience under my belt — but got stuck with this closing paragraph:

If your players wish to continue playing their characters, you can use the contents of this set to create your own adventures; the mysterious map found in area 14 of Wave Echo Cave provides one possible adventure hook, but feel free to explore other ideas using the monsters, magic items, and locations in this adventure.

Not much to go off on, so here's some general tips as well as some campaign specific ones you can leverage.

General advice

These tips apply to really any campaign but can be extra help when running published adventures as simple ways to expand from the books as written.

Foreshadow — If you have the foresight knowing you may run the campaign past the end of the book, drop hints and foreshadowing for future campaign beats. The nice thing about this is your players won't remember everything so you don't have to actually use it once it comes time to implement. Sprinkle foreshadowing all about and only use what sticks or interests your players.
Retroactively foreshadow — Sometimes you may not have the foresight to plan ahead or you just want to focus on the adventure as written. Instead, pick something the players find or do and retroactively give it meaning later. Maybe it's a random item the players find that you later decide belonged to a villain who wants it back and hunts down the players.
Unused sidequests and rumors — This is less "your own adventure" but moreso picking and chosing from the book what you want without the "burden" of having it be relevant to the main plot. Expand these side quests and give them more weight and their own plotlines. This might be the perfect way to continue if your players were focused only on the immediately important main plot and avoided side quests. They can also serve as nice palette cleansers or fillers for you to give you time to write your own adventures.
Spotlight an NPC — Give underused NPCs who had little to do in the book their own quest or story. This is a good one for writing specifically for your players based on their own experience. Every party in every campaign will have unique interactions with prewritten NPCs: an NPC wrote as a one off character might be the party's best friend.
The Bigger, Badder Evil Guy — You can always pull "the boss was working for someone even more powerful". It's a bit of a cliche but it gives your players immediate motivation and a strong tie to the new big bad. Maybe it's not just the boss's boss but a rival who's path has been cleared to expand territories. Use the villain's defeat as the spark of a new villain's rise.

Lost Mines of Phandelver hooks

The book mentions a few hooks for future play such as a mysterious map in Wave Echo Cave or the return of Glasstaff. Here's some not explicitly left by the book that I used in my campaign.

Thundertree, Reidoth & Venomfang — Thundertree is a fun side quest, but not every party will run into this rumor or choose to go on it. My party skipped on it to focus on the main plot threads, so I used it as the opening thread to our second adventure arc. Plus if you can have them fight Venomfang at a higher level, they could defeat the dragon, rather than him fleeing at half HP as the book suggests.
Leverage unexplored areas of Sword Coast — Sword Coast has a vibrant history in D&D lore and it's already fleshed out as a setting. Just on the map given in Phandelver are unused locales in the city of Neverwinter, Mount Hotenow, and The Crags, among others. You can also check out the Forgotten Realms fandom wiki for some quick location inspiration if you don't want to make up your own villages and fortresses. I set the next arc of my campaign in my own villages and dungeons within Kryptgarden Forest, an area just south of Phandalin unutilized by the book.
The Black Spider's Boss — Maybe the Black Spider was working for yet another mysterious benefactor or he was part of a group of evil mages that is pissed he's dead. Use the fact that he's a drow to your advantage: they are a footsoldier for a stronger woman in charge. I pulled this move and set up a fun drow-centric and underdark-delving adventure for my players to go on.

Whatever you decide to do, don't end the campaign because you finished the book! Let the events of your campaign be the seeds for a new adventure. Plus, it's easier than starting from a blank page.