Defining a User Interface
Overview
A user interface is the part of a program that interacts with the user.  It is usually the part that requests and presents information.  To make a good user interface, do the following
  1. Define ALL the data that your program will need to receive and present.
  2. Put yourself in the user's shoes.
  3. Decide on how you need to present and /or ask for data.
  4. Look for similarities with common programs already available.

 
Define ALL the data that your program will need to receive and present.
One of the most important things you can do is to define all the data you need to input (request from the user) and output (present to the user).
Put yourself in the user's shoes
Always remember that you are writing the program for someone (even if it's yourself).  Imagine USING the program as you design it and write it.
Decide on how you need to present and/or ask for the data.
This is where you decide on which controls will make the most sense.  Here are some clues.
  1. If the user will choose ONE of several pieces of information, use a COMBO BOX (DROP DOWN LIST) or RADIO BUTTONS.
  2. If the user will choose several pieces of related information, use a COMBO BOX with multiple selections or use CHECK BOXES.
  3. If the selection contains text that the user will type in that will be only one line, use a TEXT field.
  4. If the selection contains text that will span over several lines, use a TEXTAREA field.
 
Look for Similarities
This is subjective.  If Microsoft Office asks for a particular piece of information a certain way and YOUR program needs the same information, consider using the same mechanism.