[The Ace]

There seems to be a bit of confusion here.

Reading the Discworld in order isn't as straightforward as it sounds;

MP, Pyramids, The Truth and MR were written to stand alone.

COM, LF, Sourcery, Eric and IT are an arc.(Rincewind).

ER,WS, WA, LL, etc form a second arc, to get the best from them, these should also be read in order.(the Witches

Mort, RM, SM, Hogfather and TT form yet another story arc.(Death)

GG, MAA, FC, Jingo, FE,NW and Thud, comprise yet another series (the Watch)

Although probably not intended to originally, the Discworld has grown into a number of series, each dependant on its predecessors within its own arc. Thus, reading 'The fifth Elephant,' or 'Jingo,' before 'Guards, Guards,' would detract from these a bit.