Most people tend to use undergrads for slave labor, or simply tell them what to do to perform the protocol. In my opinion, it is far more important to focus on the big picture of their research project, and why it is exciting and relevant. If you get them excited, they will WANT to learn all of the details and, as a result, will have a much better understanding of what they're doing and perform better experiments.

I hated the using undergrads for slave labor at my PhD lab. I trained my undergrad to make sure he takes care of his dishes and only his and not do any other grad's dishes as the other grads tended to want any undergrad to wash the stuff they used.

I also think it helped to ask my undergrad to write biweekly reports on what he did, short, one-to-two pages, even if the experiments failed. It helped him better understand the protocols and how to go about DOING science.