I suppose this sounds weird, but I didn’t hear this advice from anyone when I started writing. I guess this would be the advice I intrinsically followed and would pass on to new writers:
1. Be professional. Always. Don’t print business cards on your printer. Go to vistaprint.com or printingforless.com and have them professionally printed. Design your letterhead to match. One of the things my agent told me (right after he decided to take a risk and agent me) was that I had very professional presentations. It made an impression.
2. Continue that into every area. Don’t have a website if you can’t have it look amazing. Try to make your blog different and interesting by fooling with html code. (Mine is a normal blogger template that I’ve tweaked through lots of html.
3. Look professional. When you meet with editors, agents, publishers, wear business attire. Shake hands. Look folks in the eyes. (On a side note, if you live in France, bring French chocolate!). Always, always, always write thank you notes. Always.
4. Be cautious about spouting off. This is a small industry and word travels like wildfire. Don’t gossip. Don’t burn bridges. Be courteous, kind, and teachable. You don’t want to have the professional reputation of being difficult.
5. Always answer correspondence quickly, particularly email. This shows you care about the person sending it. It will endear you to editors.