A shutter release is a helpful piece of equipment. We talked about camera shake due to handholding the camera, but even pressing the shutter button can cause blurriness. If you already own an intervalometer for capturing time-lapse photography, you can use it here as a simple release. The other option is to change your camera settings.
Setting the mirror to ‘lock-up’ before your shot will reduce the shake. Also, setting your camera on a two-second timer will help.