1. The first thing to do is actually go look at your Billing in the AWS Console - LOL. By learning how to you read your bill and find out what things mean, you'll be well on your way to saving money.
2. The second thing is to strongly consider using Reserved Instances. You can used the AWS Calculator Tool to see how much you can actually save.
3. The third thing you could take a look at is Route 53. Setting you TTL (Time To Live) for a longer period, say 10 min or 600 seconds, will greatly reduce queries to your DNS server and cut down on costs. Remember, AWS charges you for every little thing.
4. The forth thing to take a look it is your Cloud Watch metrics. If you are sending metrics from your servers to Cloud Watch too often, for example, every 1 minute to check disk usage, you could be in for big surprise when you get your bill.
5. The fifth and final thing I can think of off the top of my head is to consider using fewer ELBs (load balancers). Since an ELB can handle requests for multiple domain names you may not need a separate ELB for every application. Consider the scenario off Development, Staging or POCs (Proof of Concepts) server. Often these types of servers don't get a lot of traffic therefor one ELB may be sufficient to route traffic to multiple instances. Remember, an ELB is actually an EC2 instance so when it's running it will cost you money.

I'm sure there are many other things to take a look but these are just a few ways I could think of to immediately save you money while using AWS - Amazon Web Services.

E.