Firstly it's important to know how to recognise the 3 types of verbs, these are: Godan (Group 1 Regular Verbs) Ichidan (Group 2 Regular Verbs) Exceptions (Irregular Verbs)
How to tell the difference between Ichidan and Godan Verbs
How to change verbs into the てform
て form songs to remember how to change Godan Verbs into the てform
The 3 clips below work from ますform
This clip works from the plain (dictionary) form
Activity
Click through this powerpoint to practice changing verbs into the てform