A nice warm up is also to play the scales of a particular key using only legato, hammer on's and pull off's.

This way you are doing good left hand practice but also you are learning or reenforcing the scale shapes whcih will be very handy.

I always believe that chromatic stuff is really not the best way to go about things since it is limited in application and also doesn't provide the technique practice one thinks it will.

But it is just the other side of the coin :)