Let's see…

Lapis would give you a water weapon, which is strong against Ruby.
Ruby would give you a fire weapon which is strong against Sapphire.
Sapphire would give you an ice weapon which is strong against Amethyst (it freezes her whip or something)
Amethyst would give you her whip which is used to tie up Peridot
Peridot would give you an electric weapon which is strong against Pearl (her spear conducts electricity)
Pearl gives you her salt which can be used to manipulate Garnet into de-fusing
Garnet gives you her gauntlets which are, of course, stronger than Jasper
Jasper gives you her helmet which gives you extra defense against Lapis's water attacks

…Did I do alright?

Choose your waifu