Share 'getting dyed for the first time'

alright, so I'm going to be dyeing my hair for the first time soon, and to be honest I'm pretty nervous about the whole thing (any words of support would be much appreciated...).  Essentially I wondered if anyone had any tips for me about the whole process?  I'm gonna get it bleached and dyed professionally first time but I still feel like I don't know nearly enough about it! :(