I'm fairly new to D&D 5e, but a pretty quick study (thanks at least in part to this site!) I'll be DMing a one shot game at a family event in a couple of months. One of my players has played a similar RPG system before, but is … loose on rules in general. The rest are complete newbies, and some of them mostly want to play as a way to connect with the one who's played something else before (and is keen as a bean) rather than from their own internal initial interest. Obviously I want everyone to have a good time.
My initial thought was to run Lost Mine of Phandelver (the Starter Set campaign) seeing as I have it already, and it would give those less invested players pre-made characters if they don't want to roll their own from scratch. The problem is that it's designed to get them from 1st-5th level, and I'm not sure I want to play a game that lasts too many sessions.
After briefly considering homebrewing a one-shot (I really don't have time) I looked to see if there were any prewritten ones. (It turns out that there – are – LOTS). Many of them say they're for 3rd- to 5th-level (or some other combo) characters.
I feel like I'd like to start with the level 1 simplicity for my new players (though leveling in the game might be cool).
Does this mean that I'm limited to one-shots designed for level 1 characters, or is there an easy way to get a party of 4 or so level 1 characters through a game designed for level 3-4s?
If you feel that first-time players might do better with higher-level characters, feel free to include that in the rest of your answer.
Also, if the game goes a little long, and we need to have a second session to tie it off, that's probably fine. If it's likely to take much longer than about 6-8 hours, I doubt we'll get through it.
Best Answer
I have a fair amount of experience DM'ing for new players, so I'll give my two cents.
No, you won't be able to run a 1st level party through a 3rd-4th level dungeon/adventure
Really, you won't, unless you rebalance everything there to make it proper to 1st level. If you don't intend to spend time doing it, you simply will TPK your party. That's true even for experienced players - the difference between 1st level and 3rd level is very relevant, and a moderate challenge for a 3rd level party can one shot a 1st level party.
It's also not a very good idea to get new players to start at higher levels
Well, to be honest, the alternative is also harsh. Most new players will get confused with only their racial and 1st level features, I usually don't even recommend playing full casters to new players if they don't have time to study how their spellcasting works.
Before adding my solution, I will add some insight on my experience from published adventures, one shots and overall experience with newbie players. If you are not interested, jump to the next line splitting.
The thing with low level adventures
Usually, low level adventures (specifically tier 1 (1-4) and maybe early tier 2 (5-8)) are (quite) large, hard cover adventures for a wide range of levels. Truth is: there isn't many interesting things you can do at low levels. Things start to get interesting around 3rd level (many classes get their signatures there, others get some core features), where a one shot starting at 1st level would be ending. This means it's usually more interesting to level your characters through the entire thing and actually face a Big Bad Evil Guy at higher levels.
The thing with one shots
To actually be one shots, usually they require some experience from the players and the DM (so people don't waste time doing something that has nothing to do with the adventure). For them to be enjoyable, they require even more experience, usually. Finally, since, as I said earlier, early levels aren't exactly amazing and interesting, they are usually designed for higher levels (I'm actually impressed that you found lots of 3rd level one shots, I'm more used to at least tier 2 (5+)). Higher levels, as I mentioned earlier, are most fit for more experienced players.
That said, my sad point is: I really don't feel like D&D (or, at least, 5e) is particuarly suited for one shots for new players. You will learn lots of rules, mechanics and interactions and use it... once. There are a few simpler games that are also, as a whole system, more suited for one shots. I'm not throwing names here because I don't know your (and your party's) tastes for fantasy and whatever else, but chat and forums can help you if you are interested.
Play a 1st level one shot that has enough plot on it
Yes, they exist. Although personally I couldn't finish it in one shot, Death House (from Curse of Strahd), although being a hook (i.e. you should be playing CoS after it, not using it as a one shot) can be played as a one shot. It's designed for 1st to 3rd levels (you level to 3rd level when you finish it though, so it doesn't actually matter, you only play as 1st and 2nd levels). Important note: it's deadly. The main problem I can see with it is that the players, being newbies, will waste too much time and not actually finish it in one (or even two) sessions.
If you search enough, there should be other quick adventures for this same level range though.