How do I analyse a source for a source question or essay.

Analysing a source is the key skill needed for the study of history. An excellent method for doing this is the CABLE method.
C - Content: What is the source actually saying? This requires close reading and getting to grips with the langue used. It also requires an understanding of the context so looking at or understanding the year and what else was happening at the time is important.
A - Author: Identify the author of the piece, is this man well know? Well respect or a societal out cast? What position did he hold and was he likely to be knowledgeable about what the piece is addressing? This information fills out your understanding of what you are working with, increasing your knowledge of the context.
B - Bias: Building on your knowledge of the author and time period, what message do you think the author was trying to get across? What is he likely to tell the truth about and what is he likely to be misleading with? This is hugely important when selecting key information form a source to support an argument.
L - Left out: What is the source not saying? Building form the bias and greater knowledge of the context, what aspects of the subject matter aren't addressed? Why might this be? This is key to building the understanding of the bias as well as providing an insight into the values held by the author.
E - Exaggeration: What in the source is likely exaggerated? Can you locate another source or piece of information to back this up? This is important not only for understanding the context, but it shows what values the Author held. By what they choose to exaggerate show what is important to them in a parallel way to whats being left out showing what isn't important.
Using this method you should be able to assess and utilise a source effectively regardless of time period or type of source. It is worth noting that this principle can be applied equally to images and objects by looking at any designs and illustrations.