I agree with most of the comments here, but I'm very surprized that noone has mentioned SubVIs (OK, sorry, a small mention

.
If you have a large program that is starting to fill the screen, the BEST way that I know to simplify it is to start thinking of which parts could be best moved into a SubVI.
I beleive that moving from one large program into a programming structure that uses smaller, smarter components is the KEY step which differentiates a "rookie" programmer from a "professional" programmer.
The main reason is that creating good SubVis, or Subroutines, or Libraries requires a certain abount of forethought and planning. Developing your own set of "rules" for this is a real growth experience.
But... for somone just getting started, there are probably two easy ways to know when to create a SubVI:
1) Do you find yourself cutting and pasting code? If so, then STOP! and create a SubVI to embody the function that you are duplicating. Figure out what is common in every copy you were creating and what was changing. Put the common parts in the SubVI, and make the changing parts inputs to the SubVI. LabVIEW makes it very easy to create SubVIs. Just rubber-band ther parts that don't change and select... Edit/Create SubVI. Once you have one, personalize it with your own custom Icon and don't forget to add a description.
2) When you find yourself making one section of your program more and more complicated, to the point where you are moving things around to make space for it..... STOP!, and put that functionality into a SubVI. This way the overall program can stay simple, and the complexity can be hidden in the SubVi .. Then when you need to change the complax part, just drill into the SubVI.
Phil.