When you've decided to run or cycle to work, you'll need to do some planning ahead since you can't just carry a briefcase and wear your office clothes. Drive or take public transport at least one day a week so you can bring the things that you need to and from the office. It's good to keep a change of clothes or several at the office so you don't need to carry them with you. Consider a waterproof backpack for your laptop or any papers that you need. This works well for cycling. If you're running, transporting a laptop is not an option!
Unless you're just doing a short bike ride on a cool day, you'll probably be quite sweaty when you arrive. Don't step into a crowded elevator with your colleagues like this! Take the stairs or freshen up before you arrive. If your office has a gym and/or shower, getting clean and changed is easy. If not, see if there's a gym or community centre nearby. If that's not available either, you'll just have to make do with wet wipes, dry shampoo and deodorant. Just make sure you're smelling fresh when you walk into the office.
Be sure to allow extra time for this, so you're ready to begin work on time. You should also plan your route carefully and figure out how much time it will take ahead of time. Traffic won't affect your commute as much as it would if you're in a car, but make a note of busy intersections and factor that into your planning.
When you're running/cycling in traffic, be aware of safety issues. If it's dark early in the morning or on the way home in the evening, wear a headlight and/or flashing lights. Bright clothing and a reflective vest will also make you more visible so you make it safely to work on time.
Prepare what you need
Freshening up
Planning your time
Safe travel