There is no secret. If you're a live human being, you can probably be fit and look hot by a combination of diet and exercise. But there is a lot of confusion and wishful thinking around eating or not eating particular foods, and doing or not doing particular exercises.
Let me cut through the confusion for you. It doesn't particularly matter what you eat or what exercise you do. What really matters is how much you eat and how much exercise you do.
It's not super difficult and it doesn't take a lot of time, but it does require SOME self discipline, SOME exertion, and SOME time.
My workout consists of about 15 minutes of fairly strenuous calisthenics, at home, every morning.
I add running when I have time (I probably average 2 days per week of running). That's about it. I'm otherwise sporadically active (biking, sports, etc) but not intensely or frequently enough to compare to the impact of the daily workout. I started with a much smaller daily workout and ramped up to my current level over the course of many months.
Why every day, as opposed to the three times per week advocated by most trainers? Because in order to get enough quantity and intensity of exercise in a 3x per week schedule, I would have to work out for at least 45 minutes each time. I have a much easier time getting motivated and staying organized if I do the same workout every morning, first thing, without planning or record-keeping, no need to go to a gym, no special outfit, no equipment, no getting all sweaty. In my experience, this daily repetitive workout is effective and sustainable -- it has gotten me in phenomenal shape and kept me there for over a year now. Maybe it is not optimal in some physiological sense, but it is working very well for my lifestyle.
My current routine is:
1. 80 crunches, 60 diagonal crunches, 60 leg lifts. I do these in sets of 20 each, interleaved; so basically 20 crunches, 20 diagonal crunches, 20 leg lifts, repeat 3 times, then one last set of 20 crunches. This takes me 5 or 6 minutes. When I started, I could only do 30 crunches without really suffering, so that's what I did; I ramped up the quantity and added the other stuff as I got stronger and lighter.
2. 60 squats (AKA deep knee bends). 3 sets of 20. I added these last, starting with one set and adding sets as they got easier. Proper form is important for knee health.
3. 45 pushups (three sets of 15) plus yoga-style planking on my left, right, and middle for a 60 count each. When I started I could only do about 12 pushups, so that's what I did, and gradually ramped up to the current level. I later added the planking in an effort to alleviate lower-back pain (drastically improved, though I'm not sure whether the planking deserves the credit or not).
I interleave the pushups and squats, so I finish the crunches etc and then do one set of squats, then one set of pushups, followed by the planking, then squats, pushups, squats, pushups, done. I take a breather in between sets as necessary. Right now the whole thing takes me under 15 minutes and I don't spend very long recovering between sets. As I was ramping up, I would do fewer sets over a longer time (up to 20 minutes), due to dreading the pushups, or getting distracted with little household chores or fiddling with music or whatever.
When I started, I did 30 crunches and 12 pushups, every day, because that was what my body could handle. The key for me was to do it EVERY DAY! And to GRADUALLY increase the quantity, as my daily workout became too easy.
I run when it is convenient; between 0 and 5 times a week, averaging probably twice a week over the long haul. This is helpful for losing/maintaining weight, as well as training for sports etc.
Running is one of the most efficient converters of minutes into burned calories. But not all running is the same -- intensity matters a lot. Also, for sports training purposes, sprinting is really effective and time-efficient, and I bet it's unusually efficient for looks and weight control too.
When I run, I typically jog about three miles, sometimes more, sometimes less. The essential high-intensity part is 10 20-stride sprints. The sprints kill me much more than running more miles would, and take a lot less time. I added in the sprints after I had been jogging regularly for a while. I started with 5 sprints per run, and that was exhausting. It took me a few months before I felt ready to go to 10 sprints.
If your muscles and CV system are in shape, the other big component to being fit and looking hot is not carrying too much fat. To a first approximation, this is directly related to weight.
A couple years ago, at age 41 and 6'3", I reached body weight of around 270 pounds, eating quite a bit but being fairly active as well. I wasn't obese and I was able to play sports etc but I looked and felt big.
In contrast, at my previous peak condition around age 30, I weighed about 215 pounds, from playing soccer for 2 hours a day, 6 days a week (and eating as much food as I could manage to hold down). I looked and felt like a pro athlete. Going in to weight loss, I knew my ultimate target weight would be around 215 pounds. I've since revised it down to 210.
I don't have any systematic advice for other people to determine their target weight; obviously it will depend on physiology, goals, etc. But I find it helpful to have a specific number in mind.
0. Work out (see above). Muscle tissue burns calories much better than fat tissue, even when you're doing nothing.
1. Eat "normally" -- preferably with consistency of time and quantity from day to day. Portion size is the key variable here, based on the results of the following step.
2. I weigh myself every morning, on a bathroom scale.
3. If I'm much over 210 pounds, I know I need to eat a bit less. Adjust all portions slightly downward, and/or eliminate between-meal snacks. If I'm much under 210 pounds, I know I can eat a bit more.
4. If I'm much over 215 pounds, I need the Eat Half Diet.
This is for when I am far over my target weight for some reason. The key principle is to reduce my calories, without a lot of bookkeeping and without torturing myself.
1. Three meals per day, at consistent times. At mealtime, I eat whatever I would normally want to eat, but only a half-portion. A half-portion is generally enough to feel more or less full, eat the items I crave, and it's certainly enough to keep my activity level up. For example, breakfast might be a half-bowl of cereal with milk, plus half a grapefruit. Lunch is half a burger and half the fries, or maybe burger OR fries, but not both. Or half a burrito, or one slice of pizza (I would otherwise typically eat two slices). Or one small PB&J sandwich (not two). Dinner is similar; one bowl or moderate plate of pasta, not two; half the salad etc. I go ahead and have a steak, but only half-sized, with half the amount of potatoes (or, a whole steak and no potatoes, or no steak and full potatoes, if that's what I feel like).
2. No snacking between meals. No carrot sticks, rice cakes, no M&M's, no nothing. And no dessert. But -- no dessert is just because I'd rather eat half a burger for dinner than half a slice of cake. If I preferred the cake, I would eat that for dinner instead, and skip the half-burger. Same with the snacks. If I really wanted M&M's instead of a sandwich, I could put them in a bowl and have them for dinner. Personally I don't do this often, because I like real food and it's usually more filling, but in principle, mealtimes are my chance to satisfy my food desires, so anything goes, within quantity limits.
3. Don't drink calories! No soda, no juice, no glass of milk, no beer, etc. Again, if you'd really rather drink a full glass of OJ rather than a half-bowl of cereal with milk, then go ahead. The key principle is to moderate your calories in a simple way without torturing yourself.
Eating half makes my body hungry, and the bottom line is that it takes some motivation and will-power to stick to it. Here are a few tricks I use:
Make sure I'm working out intensely enough. Doing enough daily crunches to make my tummy slightly sore also has the effect of suppressing my appetite and making me more aware of the food in my stomach.
Use the freezer for leftovers. This is nice because if it is frozen, it's less easy to snack on, and doesn't have a looming consume-by deadline.
I brush my teeth after eating dinner. That reminds me to not snack at night.
Hungry at night? Go to bed. Look forward to breakfast, when I can eat anything in the world I want (but only a half-portion of course).
Meals not filling enough? Include an apple or other raw fruit, in place of something with less fiber & water.
Get a Soda Stream and drink fizzy water instead of snacking during the day.
Personally I eat the stuff I like, stuff that I think is healthy, plus occasional junk food and treats. I subscribe to "don't drink calories" -- I drink mostly water -- no soda, no sports drinks, and juice only if I squeeze it myself. I do like milk. On my cereal, I think of the milk as food. In a glass with cookies, I think of that as a treat, not a drink.
When I look at a piece of food, for the purposes of health/fitness I mainly see "calories". I don't pay any attention to fat vs. carbs vs. protein ratio, outside of the basic relation that fat is about 2x as calorie-dense (by mass) as carbs or protein. Your body is quite marvelous at turning any of those things into body fat or energy, as needed. I gather you do need protein for building muscle and doing repairs, but once you're grown up, you really don't need special quantities of it. And obviously you need vitamins and minerals, so I do recommend eating some fruits/vegetables/whole foods etc, but again, it's pretty hard to be vitamin-deficient outside of a very bizarre diet. The first-order effect of eating is to give your body calories so that it has energy to operate.
 cbloom has a much longer, better researched, and rantier article, that I learned a lot from.
 Aside from being one of history's most amazing personalities, Nelson Mandela has been in tremendous shape his entire life, including his decades in prison, thanks to daily calisthenics. He talks a bit about it in his autobiography, Long Walk To Freedom, although not in complete detail. It sounds like he would do 45-60 minutes which is a lot more than I do.
 I once heard Joel McHale on Marc Maron's WTF explain his workout as "Push ups, sit ups, and I starve myself."