About the selection
The main simplicity criteria: a small number of active abilities, a clear item spike, no micro-control, a forgiving right-click mechanic. All the heroes below suit every position (carry, mid, offlane, support) with a 50%+ win rate at low ranks.
After 200 games on simple heroes, move to mid-difficulty ones: Phantom Assassin, Juggernaut, Storm Spirit, Earthshaker. By 500 games — you can try Invoker or Pudge mid (if you played Pudge on support).