I am converting MP4 files to WMV with these two rescaling commands:
ffmpeg -i test.mp4 -y -vf scale=-1:360 test1.wmv
ffmpeg -i test.mp4 -y -vf s
One thing I discovered after many frustrating attempts of enhancing the final quality was that if you don't specify a bitrate, it'll use a quite low average. Try -b 1000k for a starting point, and experiment increasing or decreasing it until you reach the desired result. Your file will be quite bigger or smaller, accordingly.