There are a number of ways to save money on shipping, but they should all start at the planning stage of your project. The first steps is to determine the requirements of your shipments. You will need to determine the shipping frequency, the size and weight of your packaging, the number of different products you are shipping (and if any of them are shipped together), the locations you are shipping to, how quickly fulfilled products need to arrive, and if there are any other shipping requirements.
Once you have this data you can determine what the best carriers and modes of shipping will be for your products. Some products may be eligible for different rates on different carriers. It is helpful to be flexible on the carrier you use in order to reduce shipping costs for different products. There are also opportunities to reduce shipping costs by having the flexibility to reduce packaging as there are substantial costs savings that can be gained by reducing packaging size and weight. For example if your package weighs under 1lb it will most likely be most cost effective to send the pieces USPS first class package, but as the piece goes over 1lb the USPS shipping costs increase rapidly. You can also save money by drop shipping or comingling your shipping, but this often adds to the delivery time which may not be an option for your shipments.
It is best to layout your shipping requirements and identify areas like packaging size and weight, shipping time, and carrier service that you have some flexibility to reduce shipping costs. Once you have this information there are a number of different ways you can looking at reducing logistics costs and determine how best to manage your shipments.