Inheriting a Nikon D40 this weekend. Any Tips?

This weekend I'm getting my first DSLR - a Nikon D40 (It's a hand me down from my mom). I've only shot with point and shoots and my smartphone so I'm looking for any tips for a beginner. I've been doing quite a bit of research about ISO, Aperture, etc, and know basic things about framing and the rule of thirds, but other than that consider me a noob.

I know that the D40 is old, but it's also free and because I'm a beginner I wouldn't know what to do with a newer, more expensive camera anyway. I'm also getting a Nikkor 18-200mm lens with the camera. Any tips to help me get started?

I've heard that you should start out with a 35mm or 50mm prime lens, but I'm wondering if it would be worth purchasing one for this camera. If I really start getting into photography (which I'm planning on) I will probably be picking up a newer camera in 3 - 6 months.