Going to Rizhao by bus is easy. It takes about 2 hours and costs between 45 and 55 RMB -- buses are frequent. You can either go to the bus station located next to the train station which has at least two buses per day or head to the SiFang District or ShiBei District long distance bus stations which have several:
[SiFang] 2 WenZhou Road (main station).
[ShiBei] 58 NeiMengGu Road (just down the road 5 minutes walk).
Here is a Qingdao Public Transportation Map
that you might find useful.