We love the "Pure Faith" book. It is a small, pocket-sized book that features a "how to pray" section, as well as a wealth of different types of prayers. It is great for beginners and is easy to digest and use as a discussion point. We have extras here in the youth room; let Ruth know if you would like to take some for your group!
A few other thoughts or ideas:
Prayer Practice: Some have found it very helpful to have "prayer practice" nights. Set up a "prayerful atmosphere" (candles, dim lights to reduce distractions, etc) and walk them through various types of prayer. This can be as simple as asking them to hold a pen and paper and write down their reflections while you slowly recite the Our Father, or do some Lectio Divina sessions with them... the goal being to help them "practice" how to pray so they know what they are doing when they are by themselves.
Prayer Postures: More energetic teens might like the "Catholic Aerobics" Activity: As a group, challenge the teens to try to do all the physical actions found in the Mass in order. (Typical order for most Masses at our parish is genuflect, kneel, sit, stand, sit, stand, sit, stand, sit, stand, kneel, stand, kneel, stand, kneel, sit, stand, kneel, stand, genuflect.) Add hand gestures for a bonus round. Then you can talk about each posture or hand gesture and discuss how/why each one leads us into prayer. (For a simple article with some great explanations, click here: https://catholic-link.org/7-body-postures-praying-encountering-god/)