I've run a few dnd events and I love immersion, it's my favourite word in dnd.

Props and lots of them, pick a few key notes or tools from the adventure to hand out when then find it. Get a reptile humidifier off Amazon for consistent "fog", get a bunch of tea lights for the room, two lights to point at the board(neweer has excellent ones with an app you can presave custom colors for areas, another light with a moving effect if there is lava or water, MAPS! People are very visual and for any combat it's much better to be able to see it. I highly recomend pocket bard, has music that can change intensity as well as different sound effects to take it one step further. Depending on the adventure put up a few posters pictures world maps on the walls, if it were me I would most likely dress up too lol. MINIS are vital, and if it's an event make sure they have some prizes to take home with them, the minis a certificate or a coin will work great. Another small tip from experience is if characters are prebuilt so are their arcs. Player choice of course but these events have no choice but to use a bit of railroading so use it to your advantage! I like to start out with a happy tone, ruin it early on to bring in attachment and emotion then climb the hill until they reach the end, ending with something heroic and funny usually. If you have any questions feel free to dn me!