You need to come up with a specific plan. That plan needs to include "Learning how to do X", where X is anything you aren't already skilled in.
If you've only used Xcode to develop an iOS app, then you need to learn how to use it to make OS X apps. More specifically, you need to learn how to make OS X apps using Xcode's Interface Builder features.
If you've never used AppleScript Objective-C before, you need to learn how to do that. Google search terms:
applescript objective-c
applescript objective-c tutorial
If you've never written serial-port programs for the Mac before, you need to add that skill. If you intend to use AppleScript for serial-port access, you need to find a suitable scripting component, or figure out how to tell another program how to send and receive on a serial-port.
If all these things are the first time you've done them, then you should plan to write at least 2-4 smaller simpler programs using one facet from each, before attempting your final program. If you don't know how each individual facet or feature works by itself, then you won't be able to connect them together as a whole. Figure out each part, maybe by writing simple test programs, or maybe by modifying existing programs you find as examples, samples, or tutorials.
The principle that underlies all the above is
Break It Down. Write a plan, and break it down. Identify what you need to learn, and break it down. If you don't know how to break things down, then you should start there. The formal term is "decomposition" in a programming or Computer Science sense. So see what you can find out about that.
, I hope you'll understand).
