Here you will find some useful resources for Gospel Lesson templates for each different division in TNTT / different age groups. I have personally tried these templates in the past throughout the few years that I have taught the youth from different age groups (elementary to high school students), and I think that these templates work pretty well.
Again, simply use this as a guide and modify to fit your needs.
A reliable source to obtain the readings of the day / week are from the USCCB (United States Conference of Catholic Bishops).
When preparing for a gospel lesson, getting the gospel reading for that particular week (Sunday) should be your first step.