There's a couple of rules I live by:
1. Occam's Razor: In all seriousness, something I live by and should really get a poster to put on my cube. Occam's Razor states that the simplest explanation or strategy tends to be the best. (Wiki)
When trying to resolve a hair-pulling issue it's ALWAYS the simplest solution. Time and time again I run into the situation where my engineers will be troubleshooting an issue for hours. First by digging too deep into the issue. Then further screwing themselves when they decide to try to apply an overly complicated solution. Finally, i'm stuck trying to reverse the knots they made. I lose sleep and hair.
Computer problems are not like women. Shoot it straight and you can understand them [computers].
2. Be negative - Never tell someone that an issue will only take an hour or it'll take three. Take how much time you think an issue will take to resolve and multiply it by two. Be vague to the client, if possible, because if you tell them an issue will be fixed by 7PM, it'll be fixed by the next morning. You get it? I call it bad juju.
3. You don't have to be a computer genius to be a good IT Consultant. You just have to understand business, people, and be damn good at troubleshooting. Also, know when to stop and ask. We all know your other consultants aren't as awesome as yourself but sometimes they can offer helpful advice.
4. Google can be a savior or it can just get you into some deep shit.
-If you've ran into an issue. You're probably not the first. Unless you've recently deployed out an Exchange 2010 server, in that case you're probably screwed. Google has been a lifesaver in many instances, but since sites can't filter completely idiotic resolutions you could be getting yourself into more trouble.
That's all for now!