Here are a lot of default commands for several cases:
To use them, open Terminal (in /Applications/Utilities), then paste one of the commands into Terminal and press Return.
# Disable menu bar transparency
defaults write NSGlobalDomain AppleEnableMenuBarTransparency -bool false
# Show remaining battery time; hide percentage
defaults write com.apple.menuextra.battery ShowPercent -string "NO"
defaults write com.apple.menuextra.battery ShowTime -string "YES"

# Always show scrollbars
defaults write NSGlobalDomain AppleShowScrollBars -string "Always"

# Expand save panel by default
defaults write NSGlobalDomain NSNavPanelExpandedStateForSaveMode -bool true
# Expand print panel by default
defaults write NSGlobalDomain PMPrintingExpandedStateForPrint -bool true
# Disable the “Are you sure you want to open this application?” dialog
defaults write com.apple.LaunchServices LSQuarantine -bool false
# Display ASCII control characters using caret notation in standard text views
# Try e.g. `cd /tmp; unidecode “x{0000}” > cc.txt; open -e cc.txt`
defaults write NSGlobalDomain NSTextShowsControlCharacters -bool true
# Disable opening and closing window animations
defaults write NSGlobalDomain NSAutomaticWindowAnimationsEnabled -bool false
# Increase window resize speed for Cocoa applications
defaults write NSGlobalDomain NSWindowResizeTime -float 0.001
# Disable Resume system-wide
defaults write NSGlobalDomain NSQuitAlwaysKeepsWindows -bool false
# Disable the “reopen windows when logging back in” option
# This works, although the checkbox will still appear to be checked,
# and the command needs to be entered again for every restart.
defaults write com.apple.loginwindow TALLogoutSavesState -bool false
defaults write com.apple.loginwindow LoginwindowLaunchesRelaunchApps -bool false

# Fix for the ancient UTF-8 bug in QuickLook (http://mths.be/bbo)
# Commented out, as this is known to cause problems when saving files in Adobe Illustrator CS5 🙁
#echo “0x08000100:0” > ~/.CFUserTextEncoding
# Enable full keyboard access for all controls (e.g. enable Tab in modal dialogs)
defaults write NSGlobalDomain AppleKeyboardUIMode -int 3
# Enable subpixel font rendering on non-Apple LCDs
defaults write NSGlobalDomain AppleFontSmoothing -int 2
# Disable press-and-hold for keys in favor of key repeat
defaults write NSGlobalDomain ApplePressAndHoldEnabled -bool false
# Set a blazingly fast keyboard repeat rate
defaults write NSGlobalDomain KeyRepeat -int 0
# Disable auto-correct
defaults write NSGlobalDomain NSAutomaticSpellingCorrectionEnabled -bool false
# Enable tap to click (Trackpad) for this user and for the login screen
defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad Clicking -bool true
defaults -currentHost write NSGlobalDomain com.apple.mouse.tapBehavior -int 1
defaults write NSGlobalDomain com.apple.mouse.tapBehavior -int 1

# Map bottom right Trackpad corner to right-click
defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad TrackpadCornerSecondaryClick -int 2
defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad TrackpadRightClick -bool true
defaults -currentHost write NSGlobalDomain com.apple.trackpad.trackpadCornerClickBehavior -int 1
defaults -currentHost write NSGlobalDomain com.apple.trackpad.enableSecondaryClick -bool true

# Require password immediately after sleep or screen saver begins
defaults write com.apple.screensaver askForPassword -int 1
defaults write com.apple.screensaver askForPasswordDelay -int 0

# Allow quitting Finder via ? + Q; doing so will also hide desktop icons
defaults write com.apple.finder QuitMenuItem -bool true
# Disable window animations and Get Info animations in Finder
defaults write com.apple.finder DisableAllAnimations -bool true
# Show all filename extensions in Finder
defaults write NSGlobalDomain AppleShowAllExtensions -bool true
# Show status bar in Finder
defaults write com.apple.finder ShowStatusBar -bool true
# Allow text selection in Quick Look
defaults write com.apple.finder QLEnableTextSelection -bool true
# Disable disk image verification
defaults write com.apple.frameworks.diskimages skip-verify -bool true
defaults write com.apple.frameworks.diskimages skip-verify-locked -bool true
defaults write com.apple.frameworks.diskimages skip-verify-remote -bool true

# Automatically open a new Finder window when a volume is mounted
defaults write com.apple.frameworks.diskimages auto-open-ro-root -bool true
defaults write com.apple.frameworks.diskimages auto-open-rw-root -bool true
defaults write com.apple.finder OpenWindowForNewRemovableDisk -bool true

# Display full POSIX path as Finder window title
defaults write com.apple.finder _FXShowPosixPathInTitle -bool true
# Avoid creating .DS_Store files on network volumes
defaults write com.apple.desktopservices DSDontWriteNetworkStores -bool true
# Disable the warning when changing a file extension
defaults write com.apple.finder FXEnableExtensionChangeWarning -bool false
# Show item info below desktop icons
/usr/libexec/PlistBuddy -c "Set :DesktopViewSettings:IconViewSettings:showItemInfo true" ~/Library/Preferences/com.apple.finder.plist
# Enable snap-to-grid for desktop icons
/usr/libexec/PlistBuddy -c "Set :DesktopViewSettings:IconViewSettings:arrangeBy grid" ~/Library/Preferences/com.apple.finder.plist
# Disable the warning before emptying the Trash
defaults write com.apple.finder WarnOnEmptyTrash -bool false
# Empty Trash securely by default
defaults write com.apple.finder EmptyTrashSecurely -bool true
# Enable AirDrop over Ethernet and on unsupported Macs running Lion
defaults write com.apple.NetworkBrowser BrowseAllInterfaces -bool true
# Show the ~/Library folder
chflags nohidden ~/Library
# Hot corners
# Top left screen corner ? Mission Control
defaults write com.apple.dock wvous-tl-corner -int 2
defaults write com.apple.dock wvous-tl-modifier -int 0

# Top right screen corner ? Desktop
defaults write com.apple.dock wvous-tr-corner -int 4
defaults write com.apple.dock wvous-tr-modifier -int 0

# Bottom left screen corner ? Start screen saver
defaults write com.apple.dock wvous-bl-corner -int 5
defaults write com.apple.dock wvous-bl-modifier -int 0

# Enable highlight hover effect for the grid view of a stack (Dock)
defaults write com.apple.dock mouse-over-hilte-stack -bool true
# Enable spring loading for all Dock items
defaults write com.apple.dock enable-spring-load-actions-on-all-items -bool true
# Show indicator lights for open applications in the Dock
defaults write com.apple.dock show-process-indicators -bool true
# Don’t animate opening applications from the Dock
defaults write com.apple.dock launchanim -bool false
# Remove the auto-hiding Dock delay
defaults write com.apple.Dock autohide-delay -float 0
# Enable the 2D Dock
defaults write com.apple.dock no-glass -bool true
# Automatically hide and show the Dock
defaults write com.apple.dock autohide -bool true
# Make Dock icons of hidden applications translucent
defaults write com.apple.dock showhidden -bool true
# Enable iTunes track notifications in the Dock
defaults write com.apple.dock itunes-notifications -bool true
# Add a spacer to the left side of the Dock (where the applications are)
defaults write com.apple.dock persistent-apps -array-add '{tile-data={}; tile-type="spacer-tile";}'
# Add a spacer to the right side of the Dock (where the Trash is)
defaults write com.apple.dock persistent-others -array-add '{tile-data={}; tile-type="spacer-tile";}'

# Disable shadow in screenshots
defaults write com.apple.screencapture disable-shadow -bool true
# Disable Safari’s thumbnail cache for History and Top Sites
defaults write com.apple.Safari DebugSnapshotsUpdatePolicy -int 2
# Enable Safari’s debug menu
defaults write com.apple.Safari IncludeInternalDebugMenu -bool true
# Make Safari’s search banners default to Contains instead of Starts With
defaults write com.apple.Safari FindOnPageMatchesWordStartsOnly -bool false
# Remove useless icons from Safari’s bookmarks bar
defaults write com.apple.Safari ProxiesInBookmarksBar "()"
# Add a context menu item for showing the Web Inspector in web views
defaults write NSGlobalDomain WebKitDeveloperExtras -bool true

# Enable the debug menu in Address Book
defaults write com.apple.addressbook ABShowDebugMenu -bool true
# Enable the debug menu in iCal
defaults write com.apple.iCal IncludeDebugMenu -bool true
# Only use UTF-8 in Terminal.app
defaults write com.apple.terminal StringEncodings -array 4
# Disable the Ping sidebar in iTunes
defaults write com.apple.iTunes disablePingSidebar -bool true
# Disable all the other Ping stuff in iTunes
defaults write com.apple.iTunes disablePing -bool true
# Make ? + F focus the search input in iTunes
defaults write com.apple.iTunes NSUserKeyEquivalents -dict-add "Target Search Field" "@F"
# Disable send and reply animations in Mail.app
defaults write com.apple.Mail DisableReplyAnimations -bool true
defaults write com.apple.Mail DisableSendAnimations -bool true

# Copy email addresses as `foo@example.com` instead of `Foo Bar ` in Mail.app
defaults write com.apple.mail AddressesIncludeNameOnPasteboard -bool false
# Enable Dashboard dev mode (allows keeping widgets on the desktop)
defaults write com.apple.dashboard devmode -bool true
# Reset Launchpad
[ -e ~/Library/Application Support/Dock/*.db ] && rm ~/Library/Application Support/Dock/*.db
# Disable local Time Machine backups
hash tmutil &> /dev/null && sudo tmutil disablelocal
# Remove Dropbox’s green checkmark icons in Finder
file=/Applications/Dropbox.app/Contents/Resources/check.icns
[ -e "$file" ] && mv -f "$file" "$file.bak"
unset file

# Kill affected applications
for app in Safari Finder Dock Mail SystemUIServer; do killall "$app" > /dev/null 2>&1; done
echo "Done
. Note that some of these changes require a logout/restart to take effect.”

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