In my limited experience it always seemed to come down to what number makes every one equally uncomfortable but that can be sold to their respective parties. I guess a big part comes down to the companies funding method and the reason for the valuation.
I am actually building a valuation / feasibility study platform (not really done with it: https://www.frontfigure.com/ ). So based on my experience for tech startups, the best quick method is to do a T+1 revenue multiple, that means your next 12 months forecasted revenue multiplied by a revenue multiple of your industry and country / comparable companies. At the end of day, this would only imply a fair valuation, but then the actual valuation agreed upon would be based on the negotiations and other terms agreed upon. Good luck Bahaa