The first part this year is a 5 mark question that is pure comprehension of the sources given. (DON'T give an answer outside those sources - unless it is in the sources it can't be given marks - I have seen many students over the years write a correct answer but because it wasn't in the appropriate sources they couldn't be given any marks for it)
The next part will require you to use two or three of the given sources AND your own knowledge about any part of the syllabus. The big area where students fall down here is that they don't use all the specified sources and the marking criteria is rigid here - failure to use all specified sources and own knowledge will cost marks. The simple answer will go source A, Source B and then own knowledge but the top range answers will answer the question asked and then support parts of that response from the given sources.
The last part is the reliability, usefulness and perspective question relating two of the given sources to an aspect of the syllabus. Again areas where students fail to meet the criteria are by not showing an understanding of the topic to which the sources relate and therefore simply say 'source c is reliable' without relating its reliability to the topic mentioned in the question. Make sure that you cover reliability, usefulness and perspective of both sources as missing any one of these rules you out of the top band. Discussion of origin, content, audience etc needs to be related to the words reliability, usefulness and perspective.
I last marked WWI in 2002 but I have no reason to believe that the marking has changed much (especially as I have been a judge since then and know that the marking criteria hasn't changed).