Several people I know have tried to watch one piece again, however they failed, got bored, wanted to do other things, only wanted to see new things etc. So for them and for myself I have made a list of everything one piece, the anime, the filler, the movies, the specials, the ova etc. And in the order you should watch it to get the most enjoyment out of it. Please remember that this list includes everything and is based on my personal likes and feel of enjoyment. So without further a due for anyone who thinks about rewatching one piece here is my list.
Watching one piece again, List
One Piece Episodes 001-278
One Piece Episodes 284-290
One Piece Episodes 293-302
One Piece Episodes 304-324
One Piece Special 01 Adventure in the Ocean’s Navel
One Piece Special 02 'Open Upon the Great Sea! A Father's Huge, HUGE Dream!'
One Piece Special 03 Protect! The Last Great Performance!
One Piece Special 04 The Detective Memoirs of Chief Straw Hat Luffy. (Grand Jipangu storyline)
One Piece Episodes 291-292 'Boss Luffy Returns! &' 'The Great Mochimaki Race to the Castle!
One Piece Episode 303 'The Criminal is Boss Luffy? Chase the Vanished Great Sakura Tree'!
One Piece Episodes 406-407 'Special Historical Arc Boss Luffy Appears Again' Thriller Company’s trap
One Piece Episodes 279-283 Strawhat’s Past including Mugiwara Theater
One Piece Episodes 325-335
One Piece Episodes 337-405
One Piece Ova 02 Romance Dawn Story
One Piece Ova 01 Defeat him? The Pirate Ganzack!
One Piece Episode 336 'Chopper Man Departs! Protect the TV Station by the Shore
Movie Connected Animated Short 01 Jango’s Dance Carnival
Movie Connected Animated Short 02 Dream Soccer King
Movie Connected Animated Short 03 'Take Aim! The Pirate Baseball King
One Piece Episodes 408-425
One Piece Episodes 430-491
One Piece Episodes 493-516
One Piece Ova 03 Strong World Episode 0
One Piece Episodes 426-429 Little East Blue Arc
One Piece Episode 492
One Piece Movies 01-11
One Piece Episodes 517-
note: the first 11 movies are last before thetimeskip since they take the longest time watching.