to be honest, i feel like the only reason why you get the impression that these areas look bad is because they're not fully decorated yet! when i first started playing i planted a lot of trees because i felt like my island is lacking when the issue wasn't the trees but the amout of things around them - which was almost none and the space felt empty which made me feel like i should have more trees. and just like people above, i also don't have any specific "formation" for planting trees - i move them around until i feel like they look good to me.

another thing that i can definitely recommend, that i found out about recently, is buying saplings at nook's and then planting a fruit right behind them at certain stages of their growth which, to me at least, looks very aesthetically pleasing in the end! plus, the areas will feel more open and not much will be covered!
here's a tutorial on how to do it because i feel like my explanation might not be enough lol.
good luck with whatever you end up doing! i'm pretty sure it will end up looking amazing anyways!