What is the best way to increase negative camber in the front end.

From RPRWiki

You can buy a camber plate from OPM Motorsports (expensive) or you can bolt on the lower arms from a first gen. Integra that you can buy from a junkyard (cheap). The Integra arms are a little longer than the CRX arms so you get about 1 degree of negative camber that way, but you have no real adjustment. The camber plates give you the option to dial in as much or as little camber as you want.