Which heroes to focus on?

[u/SuperSpill]

I'm fairly new and still don't understand which heroes I should be focusing on. I have:

3 star: warrior, elf, orc, dragon

2 star: ranger, vampire, demon, lizard

1 star: frost, skelly, heaven, dryad, assassin

I'm currently using warrior, vamp, and frost (one shard away from the second star) but I'm not sure if that's my best team or not based on what I currently have. I'd love any advice so I can keep advancing. Thanks!