Sketchup is not a AutoCAD replacement nor is it really much like it. It is a 3D modelling tool and very quick and easy to use at that, but for doing orthographic drawing its not great. I should know as thats what they got me doing at the mo.
Saying that if you must. First set up your units probably millimetres then go up to camera and turn off perspective this will give you your 'orthographic' view (note its not true orthograhic, you can still orbit around it)
Personally I'd turn off the lineweigths this is done in styles, as is your background colour.
Highlight right click make group is useful for not getting all tangled up.
Hope tyhat helps, there are alot of tutorials online, as well as a communinity.