Giving a test lecture, what should I keep in mind?
Off the top of my head, things that are different about a lecture rather than a presentation:


You're not simply relating stuff you did to your peers : You're teaching people who know less about the topic than you do (even if you only know what you got from the textbook when preparing!). So think carefully about the intended audience, and how to explain the concepts at the right level. This will take time. Fortunately...
You have time. You have an hour or more rather than (say) 15 minutes. This means you need to convey less content per minute, and you can spend more time building understanding step by step. Try to think about helping your students to develop a mental model that they can fit the new concepts into, rather than just telling them facts.
Because the students are having to assimilate completely new concepts, don't overcomplicate - keep the necessary cognitive load to a minimum by omitting unnecessary details. Don't lie to them, but it's OK to say, for example, "this is a simplification, but it's a useful way to think about it at this level. We'll come back to it in more detail later.". 
Because you have more time, you'll also need to think more about (and spend more time on) structure. Think about pacing - don't talk for an hour. Instead, especially if you have a relatively small class, try to get some discussion going, or set an exercise. This may not be applicable for a demo lecture during recruitment, though.


If you have a small group (&lt;25 or so, as may happen for postgrad courses) then it's more like a lesson than a lecture and things can be far more interactive.