first off the object info box will become your friend as it allows for my precise placement of verts and objects. if you doing what i think your doing then to find the vert position you'll have to click and hold to point edit box (see pic)
and select vertexes. now select the vertex on your model and the object info box will display the verts x,y,z coordinates. if you want to place a vert in a certain place where there are no verts the using a reference vert can help. i do this be make a new cube or whatever and moving one of the verts around to where i want it and writing down the corrdinates. also worth noting is object info box can be applied to whole objects, edges and faces in which the size and rotation info in the object info box can greatly help you to form your meshes.
other little trick include the weld vertex button, it join two verts on the same line in an average location i.e. the middle which kinda sucks but can be worked through. there is also the slice button, it only works for edges and faces. what this dose is create a new edge or face from the selected one after which it can be moved along the intersecting edges lengths, (to do this hit the slice button, and then hold down the mouses left button to move it into position) after which you can the individually move the lines around. and finally there is the lock x,y,z buttons. these constrict movement of anything from view point, verts, edges, faces, objects so one to only the selected direction. so say you only want to moving something along the X direction then you would de-select y and z and now the object only moves along X which is typically forward and backward.
so i hope this helps some if its stuff you didn't already know.
