Back in November 2007, someone challenged me to list five pieces of advice I'd give to managers on my deathbed. I'm re-running that post because I like it.
1. Look for trouble. Assume things will go wrong and poke around to find out what they might be. You'll often uncover problems this way and have an earlier chance to fix them. Ask questions; don't wait for problems to come to you.
2. Do what you say you're going to do, by when you say you're going to do it, or update people accordingly. (A subset of this: Be responsive. If people have to follow up with you to get a response, you're not being responsive enough. It only takes 30 seconds to write, "I won't have time to look at this until next week." If nothing else, let people know where things stand.)
3. Ask for help when you need it. If you're overwhelmed, confused, exhausted, do not suffer in silence. A good boss will want to hear from you if you're approaching the end of your rope.
4. Be honest with your staff about the hard things. Even if you're uncomfortable addressing shortcomings, tell them where they can improve. Don't value your own comfort over their ability to grow and improve. And if deep down you don't believe they can succeed in their current position, talk honestly with them about that too.
And along the way, treat people with compassion, even in the hardest moments, like terminating someone. Don't assume anyone is stupid, insubordinate, or unmotivated; at worst, they are miscast (to steal a phrase from the great Marcus Buckingham). Truly believe this, because doing so will magically change the entire tenor of the experience for both of you.
5. You can't give too much positive feedback, as long as it's sincere. Seriously. It's like handing out chocolate. Take a minute right now to send a positive email or make a positive comment. Trust me, that email will be read over and over. You can make someone's day with only one minute of your time.