Memory aids: from kilo up, every step is ร1000 and the symbols are capitals (except k). From milli down, every step is รท1000 and the symbols are lower case. Only hecto, deca, deci and centi break the 103 pattern.
Greek/Latin roots: kilo (thousand), mega (great), giga (giant), tera (monster), peta/exa (5th/6th power of 1000), zetta/yotta (7th/8th, from Latin/Greek "seven"/"eight"); milli (thousandth), micro (small), nano (dwarf), pico (small amount), femto/atto (Danish 15/18), zepto/yocto (7th/8th again).