The first time I ran, we had a veteran player (who clearly had done it before) with us. I didn't realize some things then, but I see them now, about that player. He was awesome. I'm sharing this to give kudos to that guy, but also to illustrate how a veteran appears and can interact with people that aren't as geared/knowledgeable about the run.
First off, the group was, I think 8 noobs, 1 person that had played before, and 1 veteran guy who had a box of epic stuff.
- He loaned us weapon tokens, but not to a degree that we didn't know what to do. Loaning was good for a new person (A shiny weapon! I see what it does!); but a bunch of tokens to remember with additional functions, no. I had no concept of what a rare token even looked like, so even just being told 'red is great' by the veteran was VERY helpful. Anyway, loaning is good, but so is limiting the loaning to just a few things, and he knew this.
- He did a strange combat thing where he put his slider on the board as a backstop. At the time I had no idea what he was doing, but now I see that he was letting US defeat the monster. Good for him. I didn't realize at the time that he'd probably destroy the monster if he had attacked, and was letting us do it. I thought it was a rogue special ability! .. but he was actually assisting without actively hitting. Great choice.
Less awesome:
- He was a rogue and seemed to be looting a strange box repeatedly and we were suspicious of this, since we didn't know what it was he was doing or getting.
We thought he was stealing treasure from us (newbie assumptions!). Now I know what it was, but at the time our view was very dismal of somebody getting treasure and not telling us what, since we're used to D&D rogues that will take from the group. Hindsight says he already KNEW all the clues and was just being a rogue; I think we would have been less irritated if we had known that. I think it's super easy to forget that new players don't know all the stuff for the classes. For a new person, someone getting tokens in a box quietly in a corner while we're busy screams 'he picked a lock and stole it!' if we don't know why.
- We didn't know he'd already done the adventure. So unfortunately we mostly ignored him since he just didn't say anything. I don't know if that was fun for him to just watch us. We didn't know we could ask for info or clues -- but maybe he was having fun just watching and didn't want to interact. I don't know. I think this is maybe a downside for him: either he interacts and spoils, or just doesn't get to interact. I'm not sure what the best balance is!