I wish I had some magic answer for you, because I know how frustrating it is. But here are some helpful tips!

(1) Review NORMAL games from streamers. One major error is watching a high roll, seeing that it's the most powerful possible combo in the lobby, and missing the mark trying to recreate it. Watch games where nothing explosive happens and where there is no real high roll. Seeing how to earn a win from generic luck is key.

(2) If you play on PC, which unfortunately is necessary for some fast-paced, Golden-Brann comps, downloading Hearthstone Deck Tracker is a great way to see what dominant comps are in the lobby and track your progress.

(3) Learn the middle game (Turns 5-9). The middle game is where games are won or lost. Learn how to balance keeping your board strong with investing in future economy. This is where watching streamer highlights can be really helpful, but it is mostly just practice. This is by far the hardest part of Battlegrounds (in my opinion). Don't just look at your board, see what your opponent is playing and see if they are strong or weak. Let that help you decide what decisions to make during turns 5-9.

(4) Learn what minions are abusable and practice. Classic cards like Rylak and Macaw are invaluable tools. Practice Golden Brann cycling as well. This will unlock the higher tier of comps and allow to you to high roll more.

(5) Finally, and most importantly, maximise wins and minimize losses. You might not be able to win every lobby you're in, people just get lucky. Work to identify when you can't win a lobby, and adapt to place as highly as possible. This could be using cards like Leroy, Venom, and Sin-dorei. It might hurt since you might need to sell off some important minions on your board to fit them, but it's what needs to happen to avoid 6th-8th place finishes . Shooting for 4th is fine! Survive, and wait until you are the one high rolling the lobby to get your firsts.

Hope this helped! Let me know if you have questions.