I always like to feel what's good in the meta and also play every currently famous deck, to see what their weaknesses are. If you then start your own deck, you can slowly build your way towards countering the meta.
I think the most important part is just doing it often, you natuarlly get better then.
Also playing 14 hours(???!!!) seems a lot; a lot of times you get better if you sleep a lot and take a lot of breaks.
Also another important thing is to not hold on too tight to some cards. Like e.g. Wand Thief seems like a very good card in a lot of mage decks, that feature minions. But sometimes it just doesn't really add up towards your general plan, although not being awful. Just keep tweaking and testing and you'll get better.
Also, playing your same deck over and over is important, too. B/c you get better in how this deck plays; not always straight forward.
Hope you'll have some future success with it!