Attempting to smooth my mesh while reducing poly count?

How is the structure in the mesh? If it has square polys, or at least a very neat mesh flow, you can decrease with edge loops. Takes a bit of practice to figure out exactly what to do and where to decrease, but once you figure it out, you can get a neat mesh that looks very smooth but has a fraction of the original polycount (I've started with meshes at over 500k+ and ended up with a mesh that's less than 20k that looked almost identical).

If the mesh has a square structure but is cut into triangles (first example in pic below), you can often use Alt+J to remove the triangles so you get the square polys. It doesn't always work - sometimes it doesn't remove all the edges, or removes the wrong edges, so you'll want to check through the mesh before you start doing edge loops, because you usually want to keep the original structure. If the mesh looks more like the second example with triangles that don't seem to follow a structure at all, you'll either need to fully retopologize or use other methods to reduce polys.



A couple tutorials: