Useful mplayer options:

-vo (x11|sdl) = change video output method. X11 is usually best, IIRC.
-framedrop = allow for frames to be dropped if they can't be decoded fast enough. Keeps the video playing in real time.
-cache X = Cache X kilobytes (I believe it's KB, not 100% sure) of data. Very useful when streaming.
-ao gst -ac dspmp3 = Decode mp3 using the DSP chip. Saves a lot of CPU (more CPU left for video) but has some sync problems.