What is the proper procedure to stick d hot fix crystals? i hav a sheet of them?

i dont xactly kno how to stick them...i just kno dat they can be stuck thru a hot iron,please help me in knowing its proper procedure as when i tried fixing them wid d iron but they dint stick very well,n they can just be stuck in a row, i guess as they are not scattered.what to do about it...