Already at the beginning of a PhD the question comes up how a thesis is written and when to start with writing. The structuring of the results and the good scientific writing is often a problem which needs to be addressed as early as possible. The following links will provide you some examples and helpful suggestions, how to deal with this:

How to write a thesis proposal? (by M. Stute, LDEO, USA)

How to write your thesis? (by M. Stute, LDEO, USA)

How to write a thesis? (by R. Chandrasekhar, ARCME, Australia)