The One Piece manga has a few filler sections. These are usually added to give the anime team more time to catch up or to add some extra depth to the world. However, the core plot remains intact.
I wouldn't recommend skipping any arcs as they all contribute to the overall plot and character development. But if you must, some might suggest skipping the Fish-Man Island arc if you're in a rush.
One way is to use descriptive language to flesh out settings or events. For example, describe the scenery in detail or elaborate on a character's thoughts and feelings during a moment of downtime. Another approach could be to introduce minor conflicts or challenges that don't have a major impact on the overall story arc but add some variety and tension.
A filler story's length is unpredictable. It could be as short as a single installment or as long as a series of related episodes. The main factor determining its length is often the creative decisions made to maintain audience engagement or bridge storylines.
The One Piece anime usually lags behind the manga by a considerable margin. The production of the anime takes time to catch up with the ongoing manga storyline.
One simple way is to use a clear break in the narrative. For example, you can start a new chapter or section with a line like 'Five years later...'. This gives the reader an immediate signal that time has passed.