You could involve points such as:
- Look at the nature of the source, what is it? does this affect it's reliability?
- What time was it written? does this suggest that the source has the benefit of hindsight? Is it modern to the event? what would this tell you?
- What is the source trying to do? is the purpose of it to persuade or to generally inform? what does this tell you?
- What can you infer from the source and what does it tell you about that event?
Don't know if this will help or if you know it already but i thought i would try hehe x