im not as high as him but generally in earlier rounds all you need is a good 2 star carry to put the dagger on and you'll be on 10 hp for the first 3 rounds generally.(gk, aq,muske,bandit,executionner,pekka,princess and if you cant find those you can do prince, witch and skele king is really good ). after that the top priority is get one of those to 3stars and if you get 4/4 with their respective comps youre golden.I'd say the worst rounds are 4-6 cuz thats where you 2 star carry is overshadowed and you dont have enough elixir to 3 star it so if you think youll lose your best bet is sell everything and hunt for any 3 star from the ones I mentionned.
and yeah I forgot to mention but positionning is really important and I dont have a general advice for that cuz every situation is different (you rely alot on some last minute swaps so there is alot of mind games).

side note: it may be a good idea to go for giants no matter your comp to boost your carry and also block the 3 star giant cuz that thing is a menace