Definitely get Ginger. When facing 2 front heroes that have attack symbols (the sword icon), Ginger helps slow them down.
You need a good strong frontline, because if they fall, the back line will. Don’t bother lvling Skull Crusher when you get him (unless you really have no choice).
Stars are great and all, but you won’t collect them as fast as you can promote (unless you plan on spending money), so make sure you promote your heroes to at least the first level of purple because that extra skill is very useful.
Until you get a decent amount of heroes, you’ll have no choice but to lvl less ‘common’ ones. Try to pair what you do have together so that they will compliment each other.
When setting defenses for wars, arena and tournament, don’t select a bunch of the same aspect heroes (like say all focus), try to have a variety. With the right heroes, you could very much overpower an aspect that is stronger than you, but it does put you at a disadvantage.
Focus on one very strong team and one team that’s a little less than your first, and a third weaker. You’ll want three teams total by the time you reach 70s. Always lvl your frontline first (or one of the ‘meta’ back lines such as Hex, Oasis or Princess). Your best hero should be tip priority.
Level up the Pony (easily gotten in dungeon with a bit of time invested), he is a major pita to fight against (so is Scion)-- aspect totally is necessary to pay attention to with these guys.
Don’t be upset if you get pwn, unless you plan on spending some serious amounts of cash, you really can’t expect to compete with those who do. That’s not to say you can’t pwn. Until the latest update, I was doing very well in arena (top 5 spots), but now I’m lucky if rank 20. I don’t mind though. Just try to be happy with what you can manage.
Use your diamonds for stamina and chest deals (it’s more beneficial to spend than on gold), if you need gold, refight one of the easier tournament opponents, you earn plenty there.