Use 'Faultless hot iron cleaner'. It's AMAZING. It was recommended to me on here actually.
It's a cream which you apply to the someplace then the iron is empty, hot and steam switched off. I use an old facecloth to apply. It fizzles as you rub it in but the burnt stuff comes off. Truly brilliant. Have just lent it to my mum fir hers! I got mine on eBay or amazon, bout a fiver.