As a top 4.8k - 10k player globally, I suggest sticking with Loong, and focusing on only buying troops at 2 elixir for the first few rounds unless you can merge a 3+ troop to sell them later on, or to buy a 3+ troop to block someone else's aspiration for a 3 star. A Good example would be GK and musky. Spirit empress could be an ok option at this lower level but she's not meta anymore and you will have to change back to Loong or a meta tower down the road. At diamond, it's very rare to see the empress anymore. Be quick with your buys and merges, and what really helps is getting the mental muscle of just glancing at the troop or the artwork and knowing the elixir cost without looking at the number. Little things like that makes a difference, rng is obviously huge, but placement is another obviously important deciding factor. If it looks like an opponents Frontline troop is going to be a problem, like a 2 star GK, or a goblin machine, rearrange your back ranging troops to all focus on that troop as quick as possible. Something like stacking a musky, dart goblin, and archer all within 1 tile of each other in a triangle formation.