This is the series of elements to choose from.
Basic Elements: Water, Wind, Lightning, Earth , Fire

Advanced Elements: Metal, Nature, Wood, Lave, Ice, Light, Dark, Storm

Now here are the strengths.
Lightning->Water->Fire->Wood->Wind->Earth->Lava->Metal->Nature->Ice->Light<->Dark->Storm
Lightning beats Water beats Fire beats Wood beats Wind beats Earth beats Lava beats Metal beats Nature beats Ice beats Light beats/weak Dark beats Storm beats Lightning and so on

Here are some other weaknesses that aren't part of those.
Lightning is weak to Earth
Earth is weak to Ice
Ice is weak to Fire&Lava
Fire is weak to Earth
Lava is weak to Water&Wind&Storm
Wind is weak to Lightning
Nature is weak to Dark
Storm is weak to Lava
Lava is weak to Storm
Wood is weak to Metal&Ice
Metal is weak to Storm&Water&Fire