Is it best for a teacher to set specific goals for a class? If so, how is tha best done? How often should tests be given to see if the goals have been achieved?
I agree with what bill said. What follows is therefore
very superficial.
You need to have some form of aim/goal/objective for a class. If you don't, why are you there?
Ideally the objective should be clearly measurable, for example, 'By the end of the lesson, learners will demonstrate their ability to use the form the past tense of {list of x irregular verbs} by writing six sentences about what they did yesterday'. This is measurable in that you can check the six sentences to see if they have formed the past tense correctly.
How does a good teacher correct a student without discouraging the student?
There is no simple answer to this question. Pick up ideas from colleagues and find out which ways work best with your learners.