Quick tips for newbies

Use that launch option for infinite stat and skill resets.
Simply hold Alt and click the "plus" icon on any attribute to completely clear and redistribute your build. This only works for offline characters.

To farm, kill a specific boss (like Mephisto), then Save and Exit the game to reset the world.
Re-enter the game immediately to find all enemies respawned, allowing you to repeat the kill for more loot.

Offline tip: you can increase local game difficulty by increasing number of players in settings, this will give you more loot and exp.

Restart the game after death to bring your body to city - a safe method.

Clear all quests before proceeding into the next act, always bring teleporter scrolls with you.