How do you get relaxed before having so you can last longer in bed?

wenever i have i always last 20 times longer the second time i do it because wen i hav the first time i feel really anxious to have and i know if i get rid of that feeling that i will last soooooooo much longer in bed its happened once before but i had know i dea how i did it so how do i get rid of that feeling and get relaxed??????