I had the same problem and am doing now a CELTA course to learn teaching.
One thing I learned is this:
1. Find some common mistakes in the language of the learners, e.g. the never use 'does' for 3rd person.
2. Teach this point, and do not look at other types of mistake when teaching. Let them do the work - very often they (or at least one of the group) know already the answer; make a question like When do you use 'do'? When do you use 'does'?
3. Have them doing an controlled exercise, for example filling in the right form.
4. Correct only the teaching point.
5. Have them doing a writing or speaking exercise (divide the class in partners (pairs or threes)). In this case for example, have them asking questions about habits, both of their partner (Do you often go to your grandparents?) and others (Does you brother go often to see your grandparents?). This way they develop fluency and use the grammar in context.
6. Listen-in while they speak, but have an attitude that you do not get involved. You write down any very good sentences and any mistakes on a notepad.
7. Ask everyone what the most interesting thing is they found out about their partner.
8. Write the good/bad sentences the board and ask them to correct the mistakes.
Do not only teach grammar, but also other things, like speaking, listening, writing or reading.
Reading and listening: step 1-4:
(1) Ask them to listen and what the topic or problem is in the text.; have them comparing answers; ask them what they found out and tell them if is correct or not.
(2) Have a number of questions about relevant things that can be easily found in the text (e.g. in a text about the police: When did John discover that his car was stole? answer e.g. 'The next morning.'); again have them comparing with a partner and then give answers with whole group.
* if you need to listen more than 3 times, the questions or the text are too difficult. Try easier questions.
(3) Do a speaking exercise about the same text, e.g. tell your partner if your car was ever stolen.
Hope this type of short guideline helps.