I work for consulting firms, selling both flesh-by-the-month and fixed-budget custom dev/integration. Here's what I'd like begining devs to know:
1- be presentable. Be clean, pleasant, non-threatening (agreed, that means be lame. Lame is good). You don't *have* to wear a suit and tie (though if you want to move up, you probably should), but at least clean jeans (chinos is much better) and a top with a collar (polo is OK). "Town" shoes are much better than hiking or sport shoes. Needing to express your personality by shocking others is pretty much a dead-end. It's not "look how much you need me that I can bug you by being an ass", it's "look how much I'm sabotaging myself by making my self be a problem".
2- don't be afraid to say "no" and "I don't know". And don't say anything else instead (like "yes" or "this idea/tech sucks"). If your client/boss is asking for unrealistic, impossible stuff, just say so, or at least say you need to check, don't accept. Saying you can't do something, or something is undoable, will hurt you and others a lot less than accepting and then not delivering. Also, "I can't do it" and "it's undoable" are not the same. Maybe you need help from someone else. Maybe you need training.
3- Be proactive. Learn new skills and try to help people around you. You boss mainly. If you spot a problem or a potential sale, say so. Don't make a huge issue out of it, don't get frustrated if it doesn't get top priority, but do point out issues, and if you can, solutions.
4- be patient. Many youngsters have this mental image of where they want to get, and how good they are. You'll probably get there, but not in 6 months. You *will* have to work on nonsensical doomed projects, with idiots as coworkers and bosses. That doesn't prevent you from building skills (technical, personal , organizational), networking and building up your brand...