One of the best pieces of advice I can think of for new commuters is learn basic bicycle mechanics. Learn how your bike works. Carrying a tool kit won't help you much if you don't know what to do with it.

Also, keeping a spare change of clothes at work is a good idea. Nothing like the feeling when you get to work & realize you've forgotten your pants!

What kind of bike you use, clothing, choice of lighting, tires, etc. are all personal choices. What works for one person won't for another. Half the fun of getting into commuting is discovering what works for you & what doesn't.