Don't rush side quests - return when stronger if needed
Overlevel zones for smoother progression
Focus on core defensive stats (capped resistances and life) early game
The campaign is 4 Acts plus 3 Interludes - the old 'Cruel' replay was removed in 0.3.0
Grab resistance and skill-point side quests as you progress each Act
After the campaign and Interludes you unlock the Atlas and endgame Waystones (~level 65)