The longest running manga can vary depending on how you measure it. 'Golgo 13' is another contender. It has a consistent publication record and has captured the attention of readers for a significant period. Different manga have different factors that contribute to their longevity, such as the depth of the story, the appeal of the characters, and the ability to adapt to changing reader preferences.
One Piece as a manga has a great long - running story. The world - building is amazing, with various islands, races, and characters. Naruto manga is also very good. It shows the growth of Naruto not only in power but also in his relationships and understanding of the ninja world. Another one is 'JoJo's Bizarre Adventure'. It has a unique art style and a story that spans generations of the Joestar family, each with their own 'Stand' powers.
First, study real-life running poses for reference. Then, simplify and exaggerate the key elements in manga style. Pay attention to the flow of the clothing and hair to add a sense of movement. Also, use perspective to give depth and make it look more realistic.