I wouldnt suggest ever kind of half cleaning the bike. Using just polish and a rag on a semi-dirty bike can scratch the sh*t out of the paint. You can get small dust particles and other various junk in the rag and slide them around all over the paint. Id either suggest a full washing or just leaving it until you have time for a full washing. At the very least, spray it down with water before doing anything to it.
As far as the shield, just warm water and a really soft rag or microfiber towel. If Im out riding and dont have a rag, Ill just use water and paper towels or napkins. Not the best idea, but my shield is still scratch free. Ive never needed more than water to remove bugs.