The infographic below (Credit: TollFreeForwarding) provides tips for Facebook, Twitter, Google+, Instagram, LinkedIn, Pinterest. Whilst aimed at business there are some useful pointers for everyone to take away. In short good manners are equally important online in these social spaces as they are face to face. Attributing others work should be a given. Thanking people when sharing something interesting that they have shared can be simply done using h/t (hat tip).
Note: This was produced in 2014 so daily user stats are now out of date. However the tips still stand.