How to follow up

When you assign a task to someone else or wait for their input, ask them when they think they will finish. If they say "I don't know", ask them when they will be able to estimate. Note that date in your personal notification system (e.g. Google Calendar). When the day comes, send them an email about the status of work and a new finish date estimate. If they don't answer your email within a day, call them or have a face-to-face meeting. Repeat, don't let them off the hook (!) Otherwise, many tasks are forgotten and drag on for months. I have personally experienced tasks where the initial estimate had been three weeks and were actually finished in three years, I kid you not!