how should i tell my best friend that im in love with him

well i have this huge problem im in love with my best friend who i have know since i was a kid like about ten anyway when we both started high school i realized that i was totally in love with him and that scared me but i was to chicken to tell him i love him anyway know i want to tell him that im in love with him before we both finish school but how should i tell him ? and is that a good idea i dont want to ruin our friendship