Respect. Both for your customers, community and your competitors. Just found a "non-profit" company posting links to their pages/websites across a number of their competitors Pages. They'll be deleted so they've achieved nothing positive.
In relationship business (versus transactional) - people still buy from people. So if you're an Accountant, Solicitor, Sales Consultant or a similar type of professional, you need to let people see who you are, what you're about, what you're working on - and not just expect them to uncover it. Share your knowledge, thoughts, wins, failures.
Make sure your online infrastructure (website, blog, facebook, linkedin, other profiles and e-mail signature) are all professional quality. I don't mean expensive but I do mean make sure that they are professional. A lot of professionals use GMail web addresses (I don't mean as a service, but like
gerrymahonyaccts@gmail.com) - these look spammy, cheap and avoidable (in my opinion). Similarly, some business coaches I've met use Jimdo or SiteBuilder templates that date back more than 10 years - what "could" this suggest about you - that you're not willing to invest in your own business/training/advancement.
If you're using twitter or forums where there are avatars, sporting a Man United logo instead of say your photo/logo just doesn't help. It doesn't matter what team - what you're doing is polarising people on you choice of sports team - which is bound to be contentious if not everyone likes it - but its confusing. You see this happen a lot.