Read someone else's diary!

That is, read some primary source material as the historians call it ;-) Reading a diary or a memoir can provide a wealth of contemporary information and experience on a topic. It can seem tricky to find them though. The first thing to keep in mind is that time and place matter - you're going to find a lot more diaries or memoirs of Civil War experience say than for Crusaders in the Middle Ages. The literacy rates and related factors are just so much higher in modern times. Still, you never know until you start looking.

Start with the catalog. Simple searches can be good, for example diaries civil war or memoirs world war.