on enable_vnc()
	tell application "System Preferences"
		reveal pane "Sharing"
		activate
	end tell
	
	tell application "System Events"
		tell process "System Preferences"
			set screen_sharing_toggle to checkbox 1 of row 2 of table 1 of scroll area 1 of group 1 of window 1
			
			if not value of screen_sharing_toggle as boolean then
				click screen_sharing_toggle
			end if
		end tell
	end tell
end enable_vnc

Enable Apple's Built In VNC Server

service

AppleScript