One of the first things i learned in Maya was snapping..since then an invaluable tool i never used but now cant live without when moving vertices is the set move tool to edge, it really helps to keep things planar when i am having a good fiddle!

Press W then left click, just choose axis, then when sub menu pops choose set to edge, the move manip alignes with the edge you picked so if you need to move it it keeps the normals neat!