How to straighten long hair for guys?

i have hair down to my nose. it's medium thick i think. i straighten it but it tends to curve at the end. i want my hair striaght( if you have ever seen the video rooftops by lost prophets the guy in the kitchen cooking like that straight). if you have any tips please help me. and yes i am a guy. i'm 13. i already tried turning up the heat but all that does is frizz it out. i flip it to the left if that information is of any use. when i get out the shower i flip it to the right so it will curve to the left a little but i want it alllll straight. please give me some help. :D thank you!