Normal axial resistors are not polarity sensitive and can be connected either way around. The value is marked using a colour code - see the conversion chart.
Commoned resistor networks are supplied in SIL (single-in-line) packages. The common connection is marked by a spot on the side of the package. An 8-way resistor will have 9 pins. Non-commoned resistors are supplied in DIL (dual-in-line) packages; the resistors are connected across the package, e.g. from pin 1 to pin 16 in the case of an 8 way network (see here for DIL package pin numbering).
Panel mount and PCB mount potentiometers have 3 terminals in a straight line, possibly with the middle terminal offset. The middle terminal is the wiper, and the outer terminals are the track connections. Viewed from the spindle side, with the spindle fully anticlockwise the wiper is shorted to the left-hand terminal and vice versa.
Vertical presets have the same pin-outs as described above. On horizontal presets, the wiper connection is the single pin in the middle at one end, the two at the other end being the track connections. See the diagram below for multi-turn cermets: