For example, instead of saying "I like this" or "You did a good job" it's more helpful to say "This is effective because..." Other constructive comments could start with "We wonder..." or "Did you consider..."
Entiyisweni, ematshan'weni yo vula u ku, "Xihoxo xa wena hi lexi" kumbe "A wu tiyimiselanga ku endla leswi," swa antswa ku vula ndlela leyi u titwaka ha yona - "Ndzi lava munhu la . . ." kumbe "Ndzi anakanya leswaku hi tshikana hikwalaho ka. . ."