The power of feedback for learning cannot be underestimated!
In our day-to-day lives we are constantly giving and receiving feedback. For example, in a restaurant, on a hotel review site, performance reviews at work and even in correcting our children - feedback is a necessary part of life - but also of learning!
The article attached provides you with some information on how feedback should be given to learners; it's a bit of a read but if you a take the time to get through it I think you'll find it useful.
Feedback should be given in a timely manner so that learners get it when they need it in order to progress with their learning. Also, this feedback should focus on the process of their learning (not the outcome) as well as being specific (to avoid confusion).
A simple 'well done' is not sufficient for our adult learners even if it is nice to hear from time to time!