Answer:
Always check the label instructions of the garments before ironing – or even washing – them. Segregate the apparel based on their fabrics. Some cloth materials require a 'special' setting so grouping them accordingly will help you avoid accidentally using the wrong setting.
Check the iron to be sure the base plate is clean. A Scorched build-up of starch or sizing can be transferred to clean fabrics. Take a look at your ironing board cover as well. It should be clean.