If you have no specific interests, a good place to start is one of the modern surveys. Thomas Asbridge's The Crusades (subtitled either: The War for the Holy Land or The Authoritative History etc. in the UK and US versions respectively) would be my suggestion, though there are a number of others. (Also frequently recommended are Christopher Tyerman's God's War: A New History of the Crusades and Johnathan Riley-Smith's The Crusades: A Short History.

Another approach would be to read some of the medieval historians of the crusades. A good place to start on this front would be either a general collection like the Internet Medieval Sourcebook or a collection like Edward Peters (ed.), The First Crusade: "The Chronicle of Fulcher of Chartres" and Other Source Materials. You could also approach a single text as, for example, if you are interested in the later crusades, the Memoirs of Jean de Joinville can be an entertaining read.

There are a variety of other options both in terms of primary and secondary material, but you'll need to be more specific about what you're looking for.