It seems impossible for cell iPhone 6 to avoid being scratched without protection even if you are careful enough.
The best solution is to equip it with a screen protector, this is a special product designed for you.
A-Pre-cut Protector – you do not need to cut the protector to fit your Apple iPhone 6
Provides Instant Protection from Scratches, Dust
Leaves no residue when removed
Protect your Apple Iphone 6 screen against dust and scratches with this reusable screen protector