Becki is right, students are more forgiving if you care. They'll sense it without you saying it. We've all been students, and we've all known which teachers have cared or not. I strongly recommend learning all students' names in the first class - it always has a positive effect.
Students may be equally nervous: they'll have a new teacher, and may lack confidence in their own English ability. More so if the students don't know each other. Always incorporate SvS interaction.
Channel your nervousness into paying attention to & assessing your students, reducing their nervousness, & increasing their confidence. Let your own feelings take a backseat to theirs, & focus on your students. Teaching is helping students grow - which helps teachers grow.
The teacher "explaining" things should likely be used sparingly: let students try to explain as much as possible. For me, teaching is asking questions & having students think, work, & arrive at answers. The 2 questions I ask most: "What do you think?", followed by "Why do you think that (or X)?" Like the kid always asking why. But I also teach kids; too many questions to adults may appear condescending.
As for "instructing", perhaps start with simpler activities, tasks, concepts, & lessons. This simplifies & reduces instructions, increasing student practice time. Gradually complicate in stages (not all at once), if needed. Baby steps.
Personally, I prefer repeatable tasks that also develop non-language skills. For example, when I say, "Tell me a fictional story," they improvise one. Of course, you first have to instruct them how to do that, but in later classes, no further instruction is necessary - only the command. For me, innovation is at the heart of teaching, and TEFL isn't just about TEFL.