I like to get up to D5 for the rewards. Don't care for Legend but with the stars bonus it is doable every month. The fastest way to do it is play a net deck (or modified, slightly, if you are so inclined). Can't beat them - join them. It goes quicker that way. I then do whatever I like, it's all homebrews until the end of the season past D5.
When the meta gets stale I play once every 2-3 days. I can do multiple quests in one go and don't get frustrated with it as much. Still get the exp., just more efficiently. That's where I get the enjoyment when facing the same deck for the 100th time. At least I get EXP and progress. I remind myself that they will nerf something in a few days... mini-set is coming etc. There's always something you can do to manage the frustrating aspects.
The biggest of all was already mentioned: acceptance. You will win and you will lose. 100% both of those things will happen. And there will be long streaks of win and long streaks of loss sometimes. That, too, will pass.