I used to set the brightness in low level and ma icons size to small. But whenever I reboot, it set the default brightness and icons size. Icon size I managee but I have to set the brightness to low everytime.
Go to startup Applications in the dash. Add a new startup program "Brightness Level" and add in the command line: xbacklight -set XX XX being the level you wan at boot. I think it's a 100 scale. I've set mine at 60. Best,