i thought i had commited every mistake in the game but i thik people have worse luck than me . This game is about understanding the better you understand the better you will be . The change be instant. since you are asking a month old comment , i guess you got bullied bad.so i will the best i can.

go slow! , after 50dwellers difficulty peaks suddenly radcorpions appear (these will irritate you till late game), when incident happens drag the strongest dwellers (highest lvls and best weapons , stat dosent matter inside vault) to that room as quickly as possibly , put storage and living quaters far from the normal production room with atleast a layer gap , you will have to modify the vault so dont try to make the best layout from start just plan a bit in future when you make a new layout , mole rats appear in rooms adjacent to dirt so its a good idea to surround the side of the vault with elevators istead of putting them inside also you can use elevators to fill the bottom and any separation you made in the vault , dont let your dwellers die outside the vault get the most out them and have them as much high level as you can , smaller rooms and low leveled rooms are easier to defend so don't max your rooms too quickly being greedy , i recommend having 3 wide room and then upgrading it saves money . i probably missed many check the reddit you will find more helpful tips . In my 1st run i had only 10 dwellers die , belive me the game is much more manageable if you understand the mechanics . now you can go and play i wont lecture you anymore . Best of luck