Modeling with reference image I want to create a model of a human using "Blue Prints" as reference.So when i start modeling the form of the Head i start with the Front view of the face and match the points to positions where i think they are fine.When i switch the view port to the left/right side , to give the head like the 3d form and shape the points look good on the side but back in front view they look like they're on other positions so i ajust them in front view , switch to side and yet again they're on other positions.i hope my question is understandable ^^.do you guys have any advise ? i'm a beginner , i know the basic stuff but have problems with that.
Good Reference Images and Alignment

The biggest problem about modeling 3D models from 2D reference images is the alignment of your reference images - especially when you start modeling faces. 

My advice for a beginner is to start with a "best as possible" aligned reference image. As you can see in the set of images below (from www.3d.sk) I used lines to align the prominent facial features, mainly the eyes, the nose and the mouth (The alignment is still not perfect for various reasons regarding the reference images).



Modeling Process

Although some tutorials on the internet mention that it's best to start with a base mesh for the head, I strongly suggest that you start with a simple plane at the eyes and a mirror modifier, then model the base shape of the face in front view with the least amount of vertices possible. Switch then to side view and start aligning the outer verts to the side reference. 

During the modeling process you are then going to add loop cuts and constantly switch between front and side view to align the vertices.

The best and most in-depth tutorial for beginners on this topic is this one made by Joshua Alger.

Oh, and also do not expect to get a perfectly recognizable 3D representation of the reference images the first time you do this. It'll take some time, but with enough determination you will get there.