NEVER be in a hurry to start soldering. Dip the tip of the iron in flux and let it sit till it smokes it off. When you dip it in flux again it should absolutely sizzle and boil on the tip. THAT'S when you know it's hot enough. If you try to melt solder while the iron is still heating up, the heat will travel and damage the insulation or other components, like @tntpoof mentioned. ALWAYS tin the tip before making contact with the part because the heat will travel faster to the connection.
Check this out... https://www.rctalk.com/forum/threads/how-to-solder-correctly.81520/post-801505
Posted in 2010 by our fearless leader, @WoodiE. Excellent info for the newbies, boss man.