Hi there.
Much depends on the size of the SSD, you really need to keep ~25% free space for best long-term performance. Within that basic framework, the programs that you use most should be placed on the SSD, data (inc. movies, photos, etc.) and rarely used software should be on the HDD.
Browser cache is fine on the SSD, I'd limit it to ~400MB though and don't clean it out too often, allow the natural page update cycle to control what's stored.