To add the previous post, the Statistics panel (W) is one of the most important ways to check your work, and has a lot of other uses as well.
You can use the Statistics panel to examine Points, Lines, and Poly characteristics as well as make selections to isolate specific items, such as a single texture. For example, in Poly mode, go to the Texture drop-down within the panel and select a texture. Press the adjacent "+" to select the polys with that texture and they can be cut from the layer, changed to a different texture, or made to be invisible to work on adjacent polys until restored with the \ key.
More importantly, the Statistics panel in Poly mode shows 2-Point Polys, which are normally deleted from an object (they do have special applications) because they will prevent certain operations from working, like Rounder and Bridge, --just to name two. Additionally, non-planar polys can be identified and corrected. No object is really complete until these kinds of problems are eliminated before moving to the next level. The Statistics panel is the first thing I open up after downloading a model to check its integrity. Usually, there will be 2-point and non-planar polys to fix.