Here is quick guide to set up Skim, which is a better app for this purpose.
1. InstallationSimply download and setup Skim and LyX, following their instructions.
2. Setup PDFSync SupportSkim -> Prefs -> Sync
[x] Check for file changes
LyX -> Prefs -> Output
PDF command: /Applications/Skim.app/Contents/SharedSupport/displayline $$n $$o $$t
LyX -> Prefs -> File Handling -> File Formats -> Format: [PDF (pdflatex)]
Viewer: [Custom] [open -a Skim.app $$i] (click Apply)
Repeat previous step for PDF (LuaTeX) and PDF (XeTeX)
3. Improve OutputThe text in Skim can be blurry on some systems OS X versions. You can try messing around with the font smoothing to fix that.
defaults write -app Skim AppleFontSmoothing -integer 1
worked well for me.
LinksSkim hidden preferences: http://sourceforge.net/p/skim-app/wiki/Hidden_Preferences/#system-overrides
LyX SyncTeX help: http://wiki.lyx.org/LyX/SyncTeX