Gather all your lecture notes at one place and take the time to go through them. While studying the notes, use a highlighter to mark important points that you would want the students to memorise or understand properly. At the end, make a separate list of all the key points.
In order for the study guide to be more effective and useful for the students, you would want to keep it as precise as possible. This can be accomplished by covering only the most relevant points. A lengthy study guide may not interest the students at all and they would become restless, bored and overwhelmed.
It is possible that each student in your class would have a unique learning style. For this reason, it would be best if the delivery of questions in the study guide is varied. Consider adding questions based on different formats such as true/false, multiple choice, short answer and concept mapping.
Make sure that answer to questions you include in the study guide can be found without too much difficulty. Students should be able to find answer by going through the index of their textbook.
It would be best to keep a list of page numbers on the actual textbook where answers to questions in the study guide can be found. This will enable you to locate the answer to a question without having to spend time browsing through the textbook.
When you have successfully made the study guide, get it printed. Moreover, since education is an ever evolving phenomenon, you would have to make changes to the study guide at some point in the future. This can be made easy by saving a softcopy of the study guide on your computer.