Types of Robots
If you have a LEGO Mindstorms kit, the instruction manuals provided with the kit have several different robot designs that you can build straight out of the box. These include bipedal robots (robots that walk on two feet), multi-legged robots and even a robotic arm. If you want to build a custom robot, you should consider using these pre-made designs to help inspire you as to what you want your LEGO robot to look like and do. Don't forget that you can program your robot if you use the Mindstorms kit, so think about what types of actions you want the robot to perform when you are designing it. For example, don't choose a robot without wheels for a project that requires the robot to be able to move around quickly.
Design Considerations
When you build your robot, don't forget to take into account design considerations that add both form and function. For example, if you are building a robot that you want to navigate through a series of obstacles on a flat surface, it will need either wheels, treads or legs to move, should have a narrow body (to move amongst the obstacles and not get snagged) and will need touch or visual sensors of some type to detect when it hits an obstacle. You can program the robot to back up, turn and move forward again once it hits an obstacle, which will help it navigate through the course.
Programming the Robot
Programming using the LEGO Mindstorms language is not difficult and doesn't require that you know about computer programming. It can take some getting used to, though, so you should follow the example programs that are laid out in your instruction manuals, and look for other example programs on the internet from fellow LEGO robot enthusiasts. Don't forget to experiment with your own programs, too!