It is very easy to make a perfect cup of green tea. All you need is good tea, good quality water heated to the right temperature, and the correct steeping time. These directions are usually written on the bags of tea that you receive.
The way you brew it is up to you. It might be a pot, traditional Chinese gaiwan, tea mesh ball, disposable or reusable tea bags or an infuser.
1) put the tea in the infuser
2) pour water
3) wait the suggested time
4) take the infuser out
Most of the green teas can be re-infused, but the tea leaves should be warm when re infused.
so if your tea leaves became cold it is better to discard them. In Chinese medicine cold tea leaves are considered as poison.