One of my favorite jobs in software was when I was a Product Manager for a non-profit startup. In that role I was able to impact and touch pretty much any part of the business I wanted to, it was almost like being an entrepreneur, but doing so from within an already formed company. I also led our agile software development as Scrum Master — it was awesome. I wish I had this list of advice back then.

Mike Cohn writes on the Mountain Goat Software blog:

Never commit the team to anything without consulting them first — As Scrum Master, you do not have the authority to accept change requests (no matter how small) on behalf of the team. Even if you are absolutely positive that the team can fulfill a request. Always say, “I need to run this by the team before we can say yes.” And certainly don’t commit the team to deadlines, deliverables, or anything else without first talking to team members. You may not need to talk to the whole team–plenty of teams will allow some or all members to say, “Yeah, we can do that” without a whole-team meeting. But it’s still their decision, not yours.

This is number 1 on the list, because you should never get this one wrong.