Put .lldbinit file into your home directory.
You can put your .lldbinit in other places, but then Xcode won't automatically load it. If you put it somewhere other than ~/.lldbinit, you need to source it in Xcode in the LLDB session like this:
(lldb) command source <mypath>/.llbinit
where <mypath> is replaced by the path of your .lldbinit