I use 200ml of cold water, mix a scoop of powder with my pack, water in the blender first then the pack, wizz for 10 seconds, scrape it off the sides of the blender, wizz for a minute, into a bowl and pop in the freezer for 10 minutes.
Always lump free for me and I love it, have one every evening!
Even if you get it right though some people love it while others hate it!