Documentation. Learn how to read and write it. Write it a lot, keep it up to date, and revise whatever (if any…) exists.
Event Logs. You will find out everything that is going on. Look through the logs on your desktop, then on a server. Google the first error you find (EventID and source)
Learn to effectively google and find an answer, there is a wealth of information from vendors and IT staff available to troubleshoot and walk you through any situation.
Measure twice, cut once. Before you jump into a project or effect a change, think out loud what happens. Draw it on a whiteboard. Talk with your peers. I would rather ask a stupid question than wreck my own shop on a whim.
Have a post-project review for every project. There is no such thing as a 100% perfect project. What did you do well? What did you do that could use improvement? What was learned and gained from the project?
Make a list of the priorities for IT in your business. Is email the most important thing, or is it application access? If everything goes down, what needs to be back online first?
PATIENCE. This is a virtue, and will save your life in IT. Be patient with others, technical or not. Be patient with yourself, this is a learning process. I have been doing this every day for 7 years, and am a senior-level engineer, but I still learn something new every day, and even still make a rookie mistake from time to time (there I admitted it).
Good resources to learn- Google, technet, spiceworks, eventid.net (cheap pay site; ask your company to buy it), techrepublic. I like the Microsoft Press books, they have great in depth books on every Windows topic. Watch a webinar every month, check sites like events.dell.com, events.watchguard.com etc, most vendors have quarterly seminars somewhere in your area. Even if it is a sales pitch, take some notes, and think how you could adapt new technology to your environment.
Coffee. Lots of coffee.