Install Ruby (through Chocolatey or http://rubyinstaller.org/ or whatever else if you’re on Windows)

Install a couple Sublime plugins:

• Linting: SublimeLinter + SublimeLinter-Ruby + SublimeLinter-rubocop (see docs for RuboCop on https://github.com/bbatsov/rubocop)
• Rubocop gem (if isung RuboCop) – “gem install rubocop”
• GitGutter (if you use git)
• AllAutocomplete
• BeautifyRuby – requires HTML Beautifier gem (gem install htmlbeautifier)

Update some preferences (Preferences – Settings):

{
"auto_complete": true,
"auto_complete_commit_on_tab": true,
"copy_with_empty_selection": true,
"ensure_newline_at_eof_on_save": true,
"font_size": 11,
"index_files": true,
"rulers":
[
79
],
"tab_size": 2,
"translate_tabs_to_spaces": true,
"trim_trailing_white_space_on_save": true,
"word_separators": "./\\()\"'-:,.;<>~@#$%^&*|+=[]{}`~"
}

Some great recommendations on https://mattbrictson.com/sublime-text-3-recommendations