Syntactical errors
There are many different sorts of these and responses need to vary, too.
Error in tense structures are common.  A frequently effective response is to set the utterance in a time backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical by using concept questions.  For example:
Are we talking about past, present or backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical?
Is this a recent event which changes the backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical?
Another response is to draw a time backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical to represent the events.
Gestures, such as pointing forwards or backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical for the tense are also helpful.
Other backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical errors frequently concern a single word in a sentence, such as a backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical or adverb wrong or wrongly placed.
A useful response is often to use backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical correction (counting the words in the sentence on your fingers and stopping at the problem).  From this, learners can get which word is causing the problem and can sometimes correct it.
Phonological errors:
If the learners are aware of the backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical script, that can be used to focus on, e.g., the difference between leave and live (/liːv/ vs. /lɪv/).
Errors in stress can be tackled by marking the stress on the word on the board or by tapping out the backcontextfingerfuturelinepatternphonemicprepositionpresentsyntactical on a desk.