As you have asked this question under the 'English' section, I assume your favorite subject is English. I would suggest doing a play in Biology though, you could pretend to be animals and plants and present the skit on deforestation or something like that. On English, maybe you can go for a skit having excerpts from classics of literature. Or maybe, you could do mini dramas on different authors' life. Best of luck. Hope I helped.
If you want to do a play, I would suggest 'The Bishop's Candlesticks' by Norman McKinnell or 'Villa for Sale' by Sacha Guitry. 'The Never Never Nest' by Cedric Mount is a good option if you want something humorous. Shakespeare's plays are a bit heavy, but your teacher will like it and it might gain some points. I would suggest the court scene in 'Merchant of Venice'.
according to my interest, i would do a skit in english. there are many wonderful skits of shakespeare and there many other prominent dramatistsĀ  too.if u want to do a skit based on a hollow society then u can optĀ  for villa for sale by sacha guitry and besides that there are many other interesting subjects too. if u want to do a skit about a historical event the u can choose social.and there are many other important devotional sits in tamil language also