'Good job' or 'no, that's not the way' are evaluations. Helpful to a degree, but not overly if I was the student.
A solution on the other hand, gives me somewhere to go. Correcting in this sense, is a positive approach especially when the correction comes in the form of giving a recipe for future action.
'Don't swing so much' provides a solution of course whilst 'keep your hand and racket closer to the impact point' is arguably even better.
Focus on 'do's' rather than 'don'ts' for powerful coaching interventions.