The principle of low-effort/progressively rewarding gameplay is reducing effort with progress in-game. Same effort creates greater and greater reward towards the end-game.
Some examples:
Not raising penalties with character level(such as penalty for dying)
Not raising the cost of skill with level(e.g. mana cost).
Not increasing prices for more powerful items/upgrades of same class.
Adding exponential bonuses for spent points in stats/skills instead of flat growth.
Making effort confined in flat growth(e.g. required exp to level +x vs x*1.5) instead of demanding exponential effort growth.
Opening more options/perks as the game progresses.