Put simply: As slowly as you can stand! In this regard, the scale can be your best friend or your worst enemy. Although your goal may be to see that number go down, the scale often doesn't accurately reflect what's going on in your body.
No matter your fitness level, the number on the scale can fluctuate by five or more pounds in a single day, depending on things like how much water you drink and food you eat. These changes don't mean that you've suddenly put on five permanent pounds of fat, though. For this reason, it's important to weigh yourself at the same time every day, and to take what's on the scale with a grain of salt.
When you do weigh yourself, remember that sustainable progress is usually fairly slow. Depending on how many calories you cut out of your diet and how much exercise you're getting, 1-2 pounds per week is a reasonable goal.
But sometimes, particularly if you're on a serious long-term physique transformation journey like "Possible Pat" Brocco, the scale might not budge for weeks or even months at a time, even if the mirror tells you that you're losing belly fat and adding muscle. That's OK. It's normal, in fact! Just know that over time, your consistent approach will eventually pay off. Slow loss is always the best choice. Think of it this way: The pounds didn't go on in just a few weeks, and you won't get them off in that time, either.
If that number on the scale sticks in your mind, though, it can be important to limit how often you step on it. It may also benefit you to take weekly progress photos. That way, you'll notice those small changes and feel motivated to keep going. It may also be helpful to get your body-fat percentage checked as you go, but it's not essential.
If you get really interested in strength training, you may find that the number on the scale goes up instead of down because your muscle mass is increasing. Remember, the scale doesn't always tell the whole story, so pay attention to the mirror, how you feel, and how you are performing in your workouts.
If you know you stress out about the number on the scale, stop using it! Plenty of people have success without it.