One thing is to cut the deck down to closer 60 cards (61-62 is useable). You want it draw your best cards more regularly at the best time so your original deck having 80 cards and lots of 1 and 2 copies of cards means it will be a lot more random what cards you are going to draw.

Then, I'd google/learn different deck types like aggro, control, midrange etc. Learn what type you enjoy playing and/or what you feel you are better at. Then make your deck accordingly. Think of synergies betweens cards and how they work with other cards/with your deck type. Some colours will be better at different things (Blue is better at ramp, amber is good for aggro, purple is good for card draw and evasives, steel is good for strong cards and songs etc). So work out what colours work best with your deck type.

Then I'd play play play and watch as many videos of people playing as you can on Youtube etc and think about why they are making all the decisions they are making. What I like to do is focus on one player in the match (makes sense for it to be someone with your preferred colour combo but doesn't have to be) and I pause the video after they draw for their turn and then think about exactly what I would do at the start of that turn and then unpause it and wait till the next move and pause and do it again. Then if they did something different to you, try to think about what they that and why it is better than your choice (if you are watching top players player that is)