I am going through the tedious process of applying for Probate and filling in the the wealth of IHT forms etc. I found this book a really valuable help. It is clearly set out with easily followed explantions of the intricacies of the process and the order you follow when making the journey. The draft letters are very useful and you can modify them to suit your own situation. At the end of each chapter there is a helpful summary which includes a list of the Key points.
I recommend you read through the book before starting your own journey - it is easy to follow and it can be safely skimmed through in the first stage to get an feeling of what is needed. You can quickly find the relevant sections you will need when you are filling in the Probate forms. One excellent section is the "Worksheet" which you can use to collate all the information you will need in one place. You can then copy and paste the various items into the range of IHT forms you download from the IHT website. These forms can't be saved with the information you have entered so copy, paste and print is the order of the day.
I have read two other Probate guides but I think this is the best one to choose. You don't need any specialist information, just a dogged tenacity to see it through!
Highly recommended to anyone who is going to apply for Probate.