This tip is really two fold. I just went through the 7 Habits of Highly Effective People by the Franklin Covey group and found I was already doing this, which makes it easier for me to focus on the areas I'm not as proactive in.
Number one, don't wait for someone to tell you to do something, ask. Employers like to see an employee who is proactive and taking initiative to learn and acclimate to the new environment.
Two, choose your mood. We all have those days where we feel gloomy and don't feel like working. When those days strike, it's important that we understand we can choose our mood. This is especially important in a new job where you don't want to come across as a moody person. Stay positive!