I can recommend watching some twitch streamer, like jorbs or baalorlord, a couple of times. They tend to do it during either ascension 20 or under some other restriction, but the lessons they teach will help a lot. In some cases they will expose combinations of cards that you might not have understood how well they work together, and in other cases they will show and explain cards that is good in the endgame but not very good before that. Very, very helpful.