Since I've bee writing a bit more lately, I've often struggled with when to use or not use a semicolon. Thankfully there are sites like The Oatmeal, which not only explain things well, but make things fun in the process.
The basic idea is that you can use a semicolon to join two separate statements that could stand as their own sentences, but are related to each other.
Semicolons rock; they need to be in everyones writing tool belt. Look I did it!!!
Do yourself a favor and check out the entire post over at The Oatmeal for more uses and examples.