Depending on type of aircraft it is not advisable that you fully look out of the window until end of rotation. On widebodies, your margin between not climbing and striking your tail is so narrow that you have no chance to guess your pitch by looking out of the window - you basically only see your dashboard as a line witout horizontal reference of the wings or other parts of the aircraft.
I recommend a "fading in", i.e. let your scan change from fully looking out to fully looking in in a gradual sense, like you do it during landing when approaching to minimum.
About the rotation rate:
It is widely accepted that you fly 3°/sec. On bigger aircraft and during OEI, it is slightly lower. I also heard from old school DC-9/MD-80 pilots that you should rotate fast, because if you don't get your climb attitude fast, you will not climb.