Primary sources are a key part of the historians work and will provide important points that will strengthen your argument. However primary sources are often difficult to analyse; it is impossible to not see them through our own particular and subjective lens. The examiner will want you to show that you can study these sources quickly and then demonstrate a thorough understanding.
When examining a source, run through a checklist of questions so nothing is missed out. This would include: Where is the source from? Who wrote it (was it somebody important, or propaganda etc)? What type of primary material is it (An image, a letter, a government order)? what is the purpose of the source? Does it contradict or support your point?
All these things must be kept in mind while studying sources and furthermore they have to be constantly reiterated throughout as you answer the question in order to display a solid understanding of the material. Don't be afraid to be critical, an ability to think independently and critique a source will set you apart from other answers and show an examiner that you're thinking analytically about the source. Finally, don't just write down again whatever the source has said, or narrate what the image looks like, this is an easy way to drop marks and weaken your argument.