...This is what I had to learn myself, and what I tell new paddlers now; if they listen to me then they'll find plenty of people to boat with:
Don't try to come off as an expert. Especially because you're not one and it is quite obvious to more experienced paddlers. Be a student; a lifelong learner. Respect other people's experiences. That old codger that can't do class 3 anymore might have pioneered some of the hardest runs in the Southeast. I actually have someone who comes to mind when I write that. Listen to their stories; learn all you can. Some people are walking history books in regards to paddle sports - which is still a young sport especially in the US. Impress others by the style and grace of your paddling, not your words. Again - run things with style and grace, make the hard lines look easy, and you're doing the thing - you've got the magic. That magic - it is the best feeling in the world!
Don't get caught up in the progression ladder - it's a trap. Hey, I get it. I'm a "Look at me" person, hell I am a rock musician. Here's why I'm saying it is a trap. The progression ladder, doing harder and harder runs for bragging rights, is a trap because it has no end. There is no tip-top. There will always be a harder run than the one you just did. There is no king/queen of the mountain, unless you're thinking of elite, pro boaters, who happen to be some of the most humble people you'll meet. They don't brag and they don't have to. Remember - style and grace. Mere mortals seeking bragging rights will find a rung on the progression ladder that they cannot climb - and may well lose their lives trying to climb it anyway. It's not a way to gain respect. Gain respect by styling the runs you do. If you belong on a run, there will be no question, it will be obvious. One of the best compliments anyone can give you is, "You are a much better boater than you claim to be". And besides, do you really need to risk your life to impress your office mates? Your office mates think we are ridiculous anyway. Boaters in gear look ridiculous not cool, especially in our spray skirts. No really, we do.
Help other new boaters as you gain experience, and realize that what brings people to the river can be really complex, heavy stuff. I really do think that, I've witnessed it. People come to the river, maybe without realizing that what they are seeking can be found there, because they didn't know they were looking for it. Things like confronting chaos and fear in other parts of their lives, manifested as whitewater. Maybe they have dragons to slay.
Try to be a nice person to everyone, now I am sure some people who know me are going to laugh at me saying that, because I can be a curmudgeon. I'm a combination of a stage performer and an introvert and it gets hard for me to be friendly sometimes. But try. If I can try, you can try.
Get your crew and run stuff, support each other, have great adventures, and know that they are precious people in a limited time span in your life. I say that because your crew will change; people leave the sport for many reasons, and you may well lose a friend to the river; I've had friends who have died on the river.
There are people I miss paddling with very much, but their lives changed, their interests changed or they moved away, they had kids, they got married, divorced, whatever. So cherish your time with them. It's always shorter than you think it will be.
That's all for now and I hope this helps someone, somewhere...