I could go on and on about the benefits I’ve seen from walking while working, but if you’re already convinced, there are some tips I’d recommend bearing in mind before you get strutting along.

Make sure you get a standing desk that’s fully adjustable. Your height will change between standing and walking on the treadmill, so it’s vital you can slightly tweak the height of your desk to match.
You’ll need a laptop stand and keyboard, unless you’ve got a desktop setup. On a similar note to above, save your neck from straining and your wrists from aches by raising your screen to eye level and allowing yourself to type with your arms at a 90-degree angle.
If you wear a Fitbit, strap it to your ankle. When your wrists are stable on the desk, your steps might not be counted.
Go super slow and build up speed. At first, typing and walking will feel near-impossible. Start off annoyingly slow to get used to it, then gradually build up your speed to your normal walking pace.
Get yourself a nice cup or bottle with a straw. I don’t know about you, but I find it very difficult to sip from a mug while walking, which has resulted in some spills.
Check your treadmill desk etiquette. Some people will find your bobbing around on the screen super distracting. Before you join all meetings while walking, check that the people you’re chatting to don’t mind.
Make sure you take breaks. It’s easy to get so into the motion of walking that before you notice it, you’ve been on your feet for hours. You need to have physical and mental rest time.