Play the solos as others have listed...
EA Play (gets you a free 80+ NAT), Rivalz (don’t worry about max stars right now, but you will need them at some point once the game drops), and NFL Epics.
Would note that on the epic solos, don’t play the full games. Just play the quickest solos because you only need 40 stars to unlock the Epic Player for each solo sequence. Don’t sell anything until the game drops (IMO) because right now not many people have coins, and you can’t buy anything if you don’t have coins.
EA Play or Rivalz first. I then did Level Challenges to upgrade Andre Johnson. I’m now on Epic Ronnie Lott. If you are willing to spend some, the starter pack gives you a good squad for working through challenges
I'm getting a late start on the trial and I'd really appreciate any tips on the best way to use it to get a head start on the full game. Any advice is welcome, from the best Solos to whether it's better to buy or sell before full game drops (as well as anything else you think would be helpful). Thanks in advance for any input.