What do you recommend for decreasing file size? For example a piece that is 300mb, how would you get it down to 150mb?
You need to reduce polycount (you probably have many more triangle than you need for the detail achievable in a 3d print - I assume it is for a print) In Rhino you could run the ReduceMesh command. Personally, I find Zbrush or Meshlab do a much better job at this (Mesh decimation)
Do you want to reduce just the file size or the amount of polygons of a mesh ?
Note that there are 2 different “flavours” to save a stl file, ascii and binary. The latter is usually much smaller than the first, but it is not as compatible when it has to be read by different applications.
Thank you. Since it is a NURBS file right now, just convert to mesh and then either reduce polygon count within rhino or export to mesh labs? Can I export the mesh as an stl for 3D printing?
Yes, stl is the common format for printing and is a mesh. Even if you export Nurbs to stl it will be converted to a mesh automatically (with some menu options). However, it is usually better for you to do the mesh converting first before export to stl so you can better control the quality and density (via Rhino or external software like MeshLab or Zbrush)
Instant Meshes might also work https://github.com/wjakob/instant-meshes
It is good with organic surfaces, but there is some difficulty with hard edges. It creates uniform triangles or quads so the density is consistent regardless of whether the surface is planar or curved.
MeshLab does a good job normally and it’s free.