Reduce weight slowly
It's human nature to want to lose A LOT of weight in a very short amount of time. After all, if we could get to our target weight within a few weeks or months, that would be ideal. It would be so much easier just to spend a short amount of time on an extreme diet so we could enjoy the benefits of weight loss.
Sadly, that is not the case! If your goal is to get into proper shape and actually STAY slim, you need to reduce weight slowly.
Why is that?
To understand how weight loss works, you have to understand the human body. Our bodies are NOT designed to lose weight. In fact, they're designed to pack on the pounds as much as possible. The human body is always trying to be prepared for any "emergencies"--situations with every little food or water. In preparation for these situations, it tends to store water and food, usually in the form of fat. The more fat cells the body stores, the more "prepared" it is.
Once upon a time, this was very useful. In the days when people would go for days without regular meals, having a bit of extra stored fat came in very handy. People could continue working or traveling without running out of energy, as their bodies simply consumed the excess fat they had stored.
But nowadays, there's no need for our bodies to store extra fat. We have an abundance of food all around us, and we often eat in excess. Sadly, our bodies haven't yet evolved in adaptation to this recent change in our lifestyle and eating habits. They still tend to store more fat "just in case".
When we start to lose weight, our bodies tend to react much the same way they did in cases of extreme hunger or starvation. They shut down and cling tightly to all the energy we have stored so we can "survive". It doesn't understand that we're not actually starving, but that we're just trying to lose weight.
If you want to see proper weight loss, you have to ease your body into it. Sudden weight loss will trigger the "starvation mode", and your body will essentially shut down the energy-producing furnaces and refuse to burn calories and fat. That's the main reason crash diets just don't work: they make your body start freaking out.
But when you reduce weight slowly, your body doesn't enter the starvation mode. It realizes that you're not getting as much food as you need, so it will reduce the amount of energy you burn. However, as you continue with your reduced-calorie diet and your regular exercise (particularly resistance training), your body will have no choice but to fire up those fat-burning furnaces in order to produce the energy you need. It won't go into starvation mode because it doesn't think you're starving, it simply registers a small deficit of calories every day.
This type of weight loss can be EXTREMELY frustrating, not to mention extremely slow. But that's the best way to do it. The human body can shed up to a pound per week without going into "starvation mode". However, the real trick is making sure as much of that "pound" is comprised of fat as possible. That way, you won't be losing muscle mass, but instead you'll be getting rid of the body's extra stores. It takes a lot more work and smart eating to burn off the fat instead of blood sugar (your body's main source of energy), but that's the key to effective, long-term weight loss that is sustainable.