Dear Moon Unit,
First of all, I apologise for not replying sooner. I have been ill this week.
You say your student has good conversational skills; so you will need to focus on accuracy and not fluency. Accuracy means that you focus on your student producing correct utterances; fluency consists of focusing on getting the message across without correcting every error your student makes. I suggest you take a grammar point that your student is having difficulty with and study it using your grammar book. You can then do oral practice of the point; some useful books for this are the series by Hadfield and Hadfield: Elementary Communication Games, Intermediate Communication Games, Advanced Communication Games; you could also look “Pairwork” by Peter Watcyn-Jones. These books all give controlled practice of specific language points. There are many other books available that you could use.
It’s important for you to activate any knowledge your student has; I suggest you create situations where he will use a language point naturally. You will find many interesting ways to do this in “Grammar Games” by Mario Rinvolucri; you could also try “Recipes for Tired Teachers” published by Addison Wesley.
It is important for you to correct your student’s errors. You can do this by noting down the mistakes and going over them at the end of the activity or by giving a signal each time he makes a mistake (e.g. coughing, saying mmmmm with a confused look on your face). Whatever method you choose, it’s important that the student gets the opportunity to correct himself before you give the correct answer.