Suggested settings for your Preferences.sublime-settings.

Preferences.sublime-settings

{
  // This is the ruby default
  "tab_size": 2,
  
  // Set to true to insert spaces when tab is pressed
  "translate_tabs_to_spaces": true,
  
  // This shows all your whitespace, including spaces and tabs
  // helps keep code clean and properly indented!
  "draw_white_space": "all",
  
  // Ignore .git folder
	"folder_exclude_patterns":
	[
		".git"
	],
 
  // This is really useful, no more hitting ⌘ + s
  // your tab gets automatically saved as soon as you switch to another
	"save_on_focus_lost": true,
  
  // This cleans up your file whenever its saved
	"trim_trailing_white_space_on_save": true,
	
  // Makes it clear your lines are too long!
	"word_wrap": true
}

You can edit this in Sublime Text by pressing ⌘ + ,

In Sublime Text 3 it is slightly different.
I tried to edit Preferences.sublime-settings in Preferences --> Settings - Default, but in Sublime Text 3 you are not allowed to do it any more.
You have to paste these suggested settings in Preferences --> Settings - User instead.
Every settings you write in Settings - User will override those in Settings - Default.