Organisers contactable online beforehand, and easy to identify on the day. A brightly coloured t-shirt with the convention name/logo is good for the latter.
Easy to find information on things like travel, food and venue details. I'm way more likely to show up somewhere new if I know where the best place to park my car nearby is, whether I can get a reasonably priced lunch nearby or need to bring my own, and how to find the door to the venue without having to follow the trail of nerds.
A clear explanation of how game sign-ups work. Where practical, preferential sign-up for first timers. The golden ticket I got on my first visit to Concrete Cow really helped.
Diversity in the organisation team. Obviously that one can be tricky if there's only one or two people organising it, but I find it reassuring to know I'm not going to be the only woman in the room.
(First, this is assuming that newcomers to the hobby actually want to attend conventions - Started in '82, attended first convention as a roleplayer (as opposed to a CCG player who roleplayed) in '07.)
And with that aside, assuming they do, my answer is ... I don't know! Thinking aloud, these are newcomers to the hobby; they're newcomers to convention gaming. And that can be a whole different version of the hobby can't it?
Certainly, some 'convention buddies' might be a good idea - someone to show you around, answer questions, see you through a game or two etc. Signage is also something that really helps for people to orientate themselves around a venue.
[An aside here - I often think there is an emphasis on people to be exceptionally welcoming to people new to a convention. Drag them over to your table in the bar on a Friday night etc. However there are times when you just do want to have a natter with your mates, without having to be the Host with the Most all of the time. Sharing this 'responsibility' would be a good thing.]
Maybe some pre-onboarding by the organisers? Ask the newcomers direct - what are they worried about? What do they think they might need to know?
I have seen some lovely well-meaning initiatives over the years. I've been a mentor twice for new GMs (never once, despite offering, had anything to do like...) and I was once offered an early sign-up for Concrete Cow as a 'newcomer' and nearly survived the howls of derision from the baying crowd!
I was part of the Mentoring team at two Continuums. Us Mentors would have a badge on and we were there to help newcomers navigate the convention. We would even help them find games too, as some people could be incredibly shy and were too frightened to get involved in the rugby scrum for signing up to games. Of course we could enjoy ourselves too, and play in and run games.