Use a tripod. The great thing about owning a tripod is that it turns you into a one-person film studio. Videos shot on a tripod are steady, which gives them a professional look. Just be sure to get an adapter to attach your phone to the tripod. I like the Glif, a simple $20 device for the iPhone that’s both a tripod mount and stand. If you’re working solo, record a test video first, mark where you’re standing on the floor, and then check both video and audio before moving on.
Record all the time. The best thing about using your smartphone as a video camera is that you’re never caught without it. Have a few minutes of downtime at the office? Connect your phone to a mini tripod on your desk and record a quick video. Do you interact with customers every day? Try and put some of them on camera and record a few testimonials–you can keep it raw and leave them unedited. The more you practice, the more you’ll learn.