Big six matches (Liverpool, Arsenal, Man United) are impossible for casuals. You need a membership, loyalty points, and maybe a blood oath.
Smaller league games, like against Bournemouth or Brentford? Still tricky, but more doors open. Check the ticket exchange on the official site. That’s where members sell their spare seats.
Cup games, as I said, are your friend. FA Cup early rounds? Easy. League Cup against a League Two side? You might get a whole row to yourself.