As a web developer . . . not from the aspect of ethics in the sites you create . . .
Don't bash to get work. One of the most frequent "attacks" I find in someone trying to steal my work is that they will pick one one two irrelevant items on the site to exemplify my incompetence. This only shows their weakness. Many of those customers come back, on their knees, and the effect of "negative referral" works against the basher. This is just common sense, and often called kharma.
"I don't know" is a perfectly valid answer. In stead of bull****ing your way to a cashed check, honesty will carry ten times more reward than the short term of a quick project. One of the most annoying things I see in many web message boards is "Hey I just contracted this job and have no clue how to do what they are asking." So they go online to get free advice from those who should be doing the job!
Stick to the meat, even if you're vegetarian. What do I mean by this? I will use the SEO example. SEO folks, don't take offense . . . There are companies out there that will sell "top ten positioning" for 5K or more. Some of them are steadfast, some of them have no ethics at all. I built a customer's site, after a year he calls, and says, "what the heck, I just typed in [keyword] and came up #1 out of 11 million! How did you do that?"
I did not charge him 5K. I build the site correctly, with good solid non-spammy meat. No fat. So when you approach a project, don't allow yourself be diverted by SEO, or Bells and Whistles, or Affiliate programs . . . . keep your eye on the prize, stick with the core concept, what is going to solve this client's problems with this web site.
Long term results are most important of all. I had some examples but removed them . . . the idea here is to think about what will benefit the customer, not YOU. People get antsy and just want the project "off their desk" so they take short cuts, tell them what they want to hear, button up the project in a sorry state, and never look back. Neither does the client. Doing them right the first time insures not only will they return for more business, they will refer you. Priceless.
Remain humble. If there is one thing I've learned in my 13 years of doing this, it's that the more you learn, the bigger the world gets. There's always someone smarter, faster, and better than you and will do it for less money; but more importantly, when you think you know everything, someone or something comes along that proves you still have a lot to learn. This is almost as much an "ethical" consideration as anything else: don't let your ego get in the way of your success.
Of course, there are two rules in business.
1. Don't tell everything you know.
2. See #1. :-)