If you're newer to running adventures, here's some tips from my experience over the years. Hopefully you'll find them useful.
1. Peaks and Valleys
You can't just "get to the good stuff" all the time. The good stuff is only good because it's got build-up, and it's only memorable because it ceases after. You have to have a flow to your encounters, to keep your players interested, and give the characters time to do things other than just fight things constantly.
Look at having non-combat encounters. Have the group run into people on a stag do and help them out with an epic feat for the groom-to-be, or go to the fairground and take part in tests of strength, or take on the acrobats at their own game for money. Have the party help out tracking down a local shipment of wine, leading into an interesting tale of smuggling and piracy... Downtime is just as important as combat.
2. Stand on the Shoulders of Giants
There's some great stories out there. Take nuggets of inspiration from them to build your own campaigns and give flavour and structure.
3. Run Initially Concurrent Stories
When starting a new campaign, build in some options for the players to explicitly choose things. Make sure they feel like their decisions have consequences that matter. Also, this gives replay value later on, if you reset, and other stories to tell if the group return to a location.
It's rare that only one thing would be going on in one place. Make your world live by filling it with stories for the players to choose from.
4. Take Copious Notes
Everything that happens will come back at some point. That interesting innkeeper the players met a year ago? They're going to remember his name. They always remember...
Any time the characters say anything particularly interesting (particularly if it could relate to characterisation or character arc), note it down. Make notes as to how sessions end, so the next session picks up smoothly. Don't rely on your memory - it's going to let you down at some point.
5. Triage Stories
Sometimes a campaign you've built just doesn't stick for whatever reason. Maybe the players just aren't digging the theme. Maybe it doesn't work with the way your party want to play at the moment.
Whatever the reason, be OK with changing direction. If you need to split the story to keep people interested, do it. Make sure your players stay engaged with the story you're telling. If the situation changes later, maybe you can bring that story back again later. But you need to be OK with letting go of something that's not working, however cool you think it is.
Have a list and basic description of people and items to hand all the time. For the people, make sure they've got at least one interesting character trait to work with too, so you can instantly roleplay something with them. Pick memorable people from real life or films/shows you like, and characters based on them in.
Then if you need an NPC, you can just pick someone off the list and run with them. If you need items for loot, you can pick a group of things that make sense given what just happened and go with it.
It's never not useful to have prepared for the things that you're likely to want to need, and you're always going to need more people.
You're running an RPG. Spend time working on the characters. Come up with voices for them, backgrounds, interesting stories for them. The more you flesh out the NPCs, the better your players will be about to bounce off and engage with them, and the more involved they'll be. No-one ever got upset about the death of an NPC they didn't care about.
Be yourself while you're just telling the story or running the campaign, but take the time to get into character when it's right. It'll help get your players invested in the world, and you really want them to be invested.
8. Don't be a Pain
Tabletop RPGs are a group game played with you and a group of other real human beings. If they're being a little slow, help them out. If they're not finding something, give them a hand. If they're beating your challenges too easily, up the difficulty. If they're in line for a TPK, warn them. It's up to you to make sure your players get out of the sessions what they're looking for. You have to run the group and do what you can to ensure everyone has fun. Don't get in the way of your players.
You want your games to be challenging, not murder-fests where your players all end up dead. If they TPK and they were relentlessly stupid, that's on them. If the encounter was just way too hard, or they just had a run of awful rolls, that's on you. Look after your people.
9. Let the Players do the Math
Don't go straight to telling your players about that secret door in the corner. Tell them they're in a room. Let them ask questions and discover the door. If they don't, they don't. Your players want to be engaged. Make them work for their story, but make sure you do actually give it to them.
Anticipation and pay-off is more exciting that just feeling like they're winning the whole time, and suspense only works if it feels like there's a genuine chance of failing. Remember, character and story progression (like loot) are earned, not found.
10. Set Off the Guns
If your players get a description of a particularly interesting thing (sword, wall, artwork etc), it better actually have a point to it. Make sure that, if something looks like a Chekhov's gun, you've got a way for it to go off.
Also, make sure it going off has consequences.
11. Have Courage & Faith
You're not going to get it right all the time. Sometimes you're going to put the characters in situations where it all goes wrong. Sometimes you're going to run something and it's not going to work. That's OK.
Every session is a fresh start to learn something new, tell a great story, and have fun with your friends. If you have an idea half-way through the campaign for a new direction, run with it. See what happens. Have faith in yourself, your players and the story. You'll work it out.
And most of all, have fun.
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