It can be really fun! For example...
To learn positive and negative past forms play some "blaming"-games
(words in bold could be stressed out, underlined words are negative and positive expressions)
- Say it with an angry judge expression: John, YOU took my pen!
John replies: No! I didn't take your pen. Mary took your pen!
Mary continues: No! I didn't take teacher's pen. James took teacher's pen!
- Say it as a secret or a gossip (something funny or nasty to make it more fun):
Start: You know, John ate a spider yesterday...
The student says: No, John didn't eat a spider, he ate a grasshopper!
the next student says: No, John didn't eat a grasshopper, he ate a ladybird!