Quote From cheep:

Hi betty
Having had my viva I can tell you the things which my examiners particularly liked/wanted added:

Write a thesis structure section at the start of the thesis intro/lit review just saying 'this thesis consists of four/six experimental chapters etc... chapter 1 consists of, chapter 2 relates to, chpater 3 and 4 outline etc...... all refs are in a bib at the end etc.. or whatever goes with your work.

This then tells the examiner what to expect as he goes along how it is all going to fit together etc.. My examiners loved this (I got this from a thesis i admired). Write a concise abstract for each chapter if you can. I didnt do this and it was one of my corrections even though i thought it was adequately covered in the chapter intro- they wanted beating over th head with it!
it helps also to add a summary or 'key findings' in the form of bullet points at the end of experimental chapters - make it all clear and obvious!
finally in my discussion chapter i made a flow chart at the start of how all the cahpters fitted together to answer the hypothesis and the examiners loved this as they seem to read the thesis in bits and this helped them rebrief on what it was all about and also makes your 'story' clear and justifies why you did each section of work - helps show a good flow of ideas.
It helps to get an independent who isnt into the subject too (hubby, dad friend) to read it and tell you if they understood what the thesis is going to be about even if they dont get what the technical bits are.

Failing this pick a thesis you admire written by someone in a similar field and see how they did it - could parts have been clearer and would summaries have helped here there etc..