"Orientation" literally means "facing east"—being pointed in the right direction and knowing where you're going. As a manager, you need to orient new hires by pointing them toward success and letting them know how to get there. Something this important shouldn't go unplanned. Some basics:
Put yourself in their shoes. What would you want to know on your first day? Probably facts about the working conditions, who your boss would be and what that person's like, and how to do the job to satisfy both yourself and the enterprise. New hires may have additional concerns, which you may have picked up during the hiring process. Keep these in mind as you plan orientation, remembering that one size does not always fit all.
Assign the workload. You're primarily responsible for orienting new hires, but you'll need help. Your HR department, of course, can handle enterprise-wide issues like leave and benefits. You should also task one of your trusted team members as the new hire's "sponsor" to show him the ropes about the work he'll be doing.
Covering the basics. You're well advised to divide up the content that needs to be covered in orientation into three parts. First come the big-picture issues, like the history and philosophy of the enterprise and your team's role in it. A new hire is more likely to feel a part of your work life more quickly if she knows why you're there in the first place.
Then, focus on the details of the job itself. Explain the main job functions, outline specific tasks for the first few days and set goals for the first weeks of employment. Set up a plan for daily, weekly and monthly check-in times to give the new hire a chance to ask questions and learn your expectations. He'll be anxious to know how he's doing, so watch for opportunities to give feedback. The assigned sponsor can and should handle some of this portion of the orientation; you may want to provide that person with a checklist.
Finally come the personal details that everyone needs to know—like how to find the lunchroom or where to park, or the names of the new hire's new co-workers. Some of these details will be covered by HR, but be prepared to answer questions about policies, benefits, building access and so on.