In this section, we will see how we can work the vertices individually using the tools available under the Vertex tab:
In order to have a well organized mesh, it's important to work with the centering tool that will align your selection. Using the centering tool applied to vertices is always a good idea, because vertices gives you more control at the time of selecting areas from your model. Selecting an area using polygons or edges can give you certain troubles because they are not really too precise, but vertices are. So, my advice is to use the Vertex mode with this tool:
To use it, make a selection of the vertices you want to center and click on the tool. The pop-up dialog will ask you for the axis (or group of axis) you want them aligned to. Select the one you need and click on OK. Then your selection will be aligned to the very center of the axis selected.
You also have an extra tool for this, located just under the Center Vertices tool called Center All...