The easiest way to memorize he reactivity series is to use mnemonic. Form a logic sentence or a list of names of relatives or friends where the first letter of the element of the series falls in with the first leter of the words in sentence or the names from the list.
Another way to memorize this series is to keep in mind hydrogen, included in this list though is not a metal, splits this list in two.
If the list is written vertically, keep in mind that all the metals located above hydrogen react with acids, while those found below hydrogen do not react with acids. In fact, if a metal is more reactive than another metal found within a compund, the less reactive metal will be removed from compound, the more reactive metal taking it's place.
Its on the back of the periodic table.