Okay well before we get into the specifics, it's a good first to think... "How will this file win the game?"
Fire wins by carnage and destruction, light wins by survival and outlasting, wind and water win by manipulation and playing for SP or playing to defeat the opponent's strategy, and darkness wins by timing and tricks. Lawtia's greatest strength is the ability to have huge momentum swings by well timed assaults.
So like if you look at lawtia, you will see lots of RANGE=1 units and very few archers. The strength of lawtia lies in cards like Assassin soul, Death's Embrace, Consuming Grudge, Bitter Destiny, etc. In the starter, the first thing to work on is the timing of your assassin soul (should be in the 3rd slot), and timing your shades.
Lawtia basically has a really hard time dealing with walls and combos that get set up on the field, so the best way to attack your opponent's strategy is to play your "Shades" on key turns to prevent the combo from even being set up in the first place.
Regarding your starter file in particular, a good way to begin is by going shade -> reverant -> shade -> moonlight warrior. The shades will sometimes drain SP which prevents your opponent from playing any cards, and then you will likely trigger two 1LP damage based soul skills. Those early souls are GOOD! Don't think losing LP is a bad thing. If losing LP activates powers that crush your opponents units, they might never recover. Then you can wait till another unit is about to die, and a turn ahead of time play some random lvl 1 unit to use as assassin fodder. Using assassin on the right unit can basically destroy your enemy by defeating his strategy.
Then towards the end of the game you want to get Dalos set up and hope he can carry you to victory.
The True Hero / Callonia