|-bg colorname||Background color|
|-fg colorname||Foreground Color|
|-title name||Window title|
|-geometry geom||Window size and position|
These common options are described on the X manpage. The most complicated is the geometry option which lets you choose the position and size of the window. The geom string consists of up to 4 numbers. The first 2 give the size (in characters for xterm, in pixels for just about everything else) and the following 2 give the location (in pixels). So
xclock -geom 50x50+30+40will draw a clock of size 50 by 50 at location (30,40) (where (0,0) is top-left).
xclock -geom 50x50-30-40would draw the clock 30 pixels from the right edge of the screen and 40 pixels up from the bottom.