Roast the flour well and pour the milk in slowly, as they tend to lump quickly. Ensure to whisk continuously in this process. If there are lumps, then you can pass the mixture through a blender.
Cook till the consistency is slightly thicker than bechamel sauce. Once it cools, it becomes easier to handle.
If you feel you are not able to shape them, don't worry! Just shape it like you can, dip in the egg and roll on the breadcrumbs. Allow it to rest for sometime, and while it is going to be put into oil, just slowly shape into the cylindrical. You will definitely get better looking croquettes. :)