Here are some tips and tricks that are seldom mentioned:
1. Use 'trap' defenders if ur roster is low ranked. For instance, if your opponent hasn't got a solid counter to your electro, it doesn't really matter if he is rank 3 or rank 5, they are not going to have a good time.
2. Take breaks and don't be afraid to change up your deck if it's not working for you. I was losing matches with void as he is a bit slow. So I benched him even though he is decay and brought in another defender into my deck.
3. Watch youtubers streams. Beroman, KT1, Andrewtheruff etc. They are all solid players and you can copy their strategies, rank up the same attackers/defenders that you see do particularly well for them and learn interactions or niche counters you may not have thought of,
4. Adapt your mastery setup to each meta. Again, you can copy those used by high end youtubers.
5. Practise fighting. If you think your skill could be better then always try to improve it. I got highly skilled by doing labyrinth and act 6. Sadly kabam nerfed act 6 into the ground and labyrinth is no longer a challenge since the game has progressed a long way from rank 4 5 stars. Perhaps doing abyss runs, gauntlet and eop fights and practising with different champions will help you master their playstyle.
6. Secret tip that no one mentions: At the start of the meta go in and play 10-20 matches with energy. Use attackers that you think might be able to do certain defenders and place champs on defence you don't usually place and see how they do. Then make a mental note of how it goes without any pressure of winning. Then you can get started building your deck for real with all this in mind and play with elders marks.
I haven't been able to play too much this season but it works well for me: