This is a continuation off of the previous trophy:
You should acquire plenty of Skill Posters through running Legend Log and Dream Log. The only problem with this is that many of them will end up stating that you cannot get them, due to them being upgrades to the base skills found elsewhere. Many of the Straw Hat crew have basic skills that you could acquire through simply playing as them and achieving their requirements (such as defeating a strong enemy as Zoro to unlock his first, or killing 500 enemies as Usopp for his first) which, in turn, will help in unlocking the others.
Many posters come with three skills to them, and you might even unknowingly meet the criteria for the second and third skills on a poster. Do note that it seems that only skill unlocks at a time on each poster (I had met the requirements for Usopp's second and third skills, but since the third required the second, a mission had to happen between it to let it unlock). That being said, look in the Skill Poster menu and check on which can easily be obtained (such as defeating so many enemies as such-and-such, defeating this enemy several times, or using this character in a Special Kizuna Attack) and keep that in mind when doing a Legend Log mission, or hope that they become part of your crew in a Dream Log mission.