Due to its tough and robust nature, earth release is best suited for being used defensive. Don't get me wrong, it can be used in many different ways, but it's sturdiness makes it ideal to deal with other techniques. As you said, it is indeed strong against water and weak to lightning, but sometimes the situation dictates, so alway keep in mind the size of your opponent's techniques when using earth to counter.
Earth is neutral to both wind and fire, and a mixture of them brings about the creation of entirely new elements:
Mixing earth and water chakra creates wood.
Mixing earth and fire chakra creates Lava.
Mixing earth, fire, and wind chakra creates dust.
Each of those are KG, so you don't have to worry about them for now.
With that being said, let's begin from where you left off in your previous training. Make four handseals and place your hand against the earth and channel chakra therein. This will cause a pillar of earth to rise up, and once it does you'll focus raiton chakra in this pillar in order to charge it with electricity, which will be discharged all around it and shock anyone in the vicinity.