If your USB 3 device needs a cable to sit between the computer and the device (many do, for example external hard drives) make sure that the cable is fully extended with the device as far away from the computer as possible.
Also position the USB 3 device/s as far away from your Bluetooth devices as possible. For example; if you have a hard drive, don't have it sitting next to your Bluetooth mouse or keyboard but instead in the opposite direction ideally behind the computer. If there is a USB 3 hub between the end device and computer also ensure that this and any cables attached to it are also as far away as possible from your Bluetooth devices.
If the device was supplied with a particularly short USB 3 compatible cable then you may want to replace it with a longer one. USB 3 cables can be found up to 3 meters in length so this should give you plenty of distance to better separate the device. Make sure that you buy a quality shielded USB 3 compatible cable.
What if I have stacked computer accessories that are connected together and making physical contanct, do I really need to try seperating them as well?
If you have modular computer accessories such as stackable hard disk drives then yes, absolutlely remove them from the proximity of the main computer. A good example of this are stackable accessory hard drives designed to fit on top or below an Apple Mac Mini computer. If you have such a device and it is connected to the Mac Mini using a USB 3 cable then definitely un-stack it for a few minutes to test if you're Bluetooth problems are resolved!