These Spanish Subject Pronouns Activities will help your students better understand this concept. This is something that you should make sure EVERY student completely understands before moving on since it is so important with conjugating verbs in all tenses. Start off by going through this very detailed and thorough Power Point.
After you can assess the students on the following worksheet
Make sure students understand what the Subject Pronouns even are in English, that way they can better understand how they are used in Spanish. Here are some YouTube videos that could be helpful.
Here is a parody song teaching the Subject Pronouns as a music video:
This one is also pretty good: