Other than "answer a lot of questions" and "build up a good reputation"?
For example, let's say someone has a problem, and I identify it as a well-known NP-complete problem and refer to some algorithm or algorithms. Is it bad Stack Exchange etiquette to say something at the end like "If you want to hire me to implement this, contact me via the email address on my profile"? (Yes, I know that in many cases someone else will kindly post a basic implementation free of charge so it might prove to be a waste of time to offer consulting/contracting services, but let's entertain the possibility that in a few cases, someone might be able to get some work out of it.)
Apart from that, any other do's and don'ts for consultants seeking work?