A lot of people want to lose weight; however, losing weight takes time, which is why everyone isn't a supermodel. You need to be willing to put a lot of time and effort into your workouts if you want to look thinner and trimmer. Still, you should find some exercises that burn the most calories in order to save yourself a little bit of time. Burning calories takes work: you have to sweat if you are going to burn calories, and you have to be willing to vomit if your workout is a true test of your physical limitations. This means that you need to find an exercise that you are dedicated enough to, one that you're willing to practice until you vomit, and one that is not easy in any way shape of form when you begin.
In fact, the exercises that burn the most calories are different for everyone, because they are the exercises that are most difficult for you. If you happen to be really strong when it comes to doing push-ups, doing three sets of twenty a day is not going to be as productive for you as for someone whose pectoral muscles are virtually nonexistent. You need to find the exercises that you have the most difficulty performing, or you should try new exercises that your trainer may not have shown you. For example, I started long distance running a few months ago, and lately have gotten pretty involved in it. After every run over three miles, I am tired, out of breath, and sweating buckets; this is the most physically taxing exercise that I do. I'll admit, it is painful and I have thought about giving it up, but I stick with it because I know if I try something that is difficult, I will see results.
The only way to achieve in anything is to challenge yourself. Let's use another quick example: Let's say a young woman is blessed with the extraordinary ability to multiply three-digit numbers in her head in mere seconds. How much work will she have really done if the only thing she scores well on are math tests? Not much work at all, I'm afraid, so she won't have challenged herself...and if her work wasn't challenging, then it was rather easy for her, and she accomplished nothing. It's only logical: your input varies directly to your output. What you put into your workout determines what you get out. If you shy away from doing sit-ups because they are too difficult, then you are destined to have a weak core. But if you put yourself through the pain for a few months, you will see improvement, burn many more calories than you would doing "easier" exercises, and you'll feel better about what you can do.
However, there are some exercises that when done to the right extent will make anyone sweat. For this I recommend long distance running. Even if you have great endurance already, running six miles in the sweltering heat on a course filled with hills and hard ground will make you sweat and prove to be a thoroughly taxing workout. You can always push your limits just a bit further with running as well, adding mileage each week and adding some speed work and dashes into your run. Plus, it is a great cardiovascular workout that will give you the endurance to tackle other exercises for a longer amount of time.
Another great, taxing exercise would be a circuit. Circuits are sets of exercises that are done in rounds and force the practitioner to switch between exercises such as push-ups and sit-ups in seconds. Here's an example of a circuit for you:
Start off by doing a minute of push-ups. Once done, get on your back and count out a minute of sit-ups. After that, stand and do a minute's worth of jumping jacks. Once you have done that, do another minute of sit-ups, and after that go back to another minute of push-ups. So far, this is only a five minute workout, but I guarantee that it will give you great difficulty and keep your heart rate up. If you would like to add something extra before taking a break, do your circuit workouts near a track or field. This way, you can take a quarter-mile of half-mile lap after each round, then take a short break, probably a minute but nothing more than two minutes. The more you have to catch your breath, the better your workout is for you.
Between circuits, long distance running, and perhaps some lifting (although this should be done in moderation because of the injuries it could cause if done in excess), you'll find an exercise that is very challenging for you, and that will be the one to burn the most calories. Don't let a circuit daunt you, just suck up whatever fear you have and work through it. Yes, burning calories hurts, and yes, it can make you feel ill, but we've all done some sort of challenging physical activity, haven't we? You know that when it's over, you will be okay, and you will feel much better about yourself. The best motivation you have for exercising is keeping in mind that everything will be fine afterwards, and all it requires is your best effort.