One of the biggest struggles that seem to confront people in our technologically obsessive age is weight management. Magic pills sprouting from the store shelves and advertiser's boxes, new diet and fitness fads coming and going, and countless psychological attacks from the marketing boys telling you how you should look. I've been on this train for upwards of 15 years now and I'd like to share what I've learned, as I have time to articulate.
A common illusion is that exercise is a good way to burn off energy stored as fat. This is fundamentally flawed and incomplete.
The fastest consumer of energy is tissue generation while sleeping. Depending on sources, you will burn around 5 lbs of fat to add 1 lb of muscle. Aerobic exercise is a terrible method for this, as the main drive is to increase endurance, which does not correspond with adding muscle tissue; actions like running are hard on the body's chemical reserves and will inflict more damage on the tissues than can be easily regenerated; distance runners build towards smaller, highly efficient musculature - not a good way to lose weight. Aerobic exercise is great for the vascular system and the brain, but not for dropping pounds if that's your goal.
Signalling the body to build muscle is well achieved through anaerobic exercise (weight lifting) however this is also a field fraught with poor information. Working small muscles in isolation is one pitfall; failing to adequately challenge your physiology is another. The body needs to receive a clear message - we're encountering strong resistance and need to put on more muscle to overcome the obstacles. Full-body compound lifts that engage the body's prime movers are one key, progressive overload is one more. Hormone output makes a large multiplier on the overall effort, part of why involvement of the legs in every training day is critical; circulation through the sex organs gives the best HGH and testosterone release, enhancing your efforts. Sunshine on the chest and gonads is also helpful according to research, as is testicular massage if you have 'em. Haven't done research on whether mild ovary massage is helpful for female hormone levels but I would suspect a symmetrical effect. Another common error is pushing too hard - working out "because it feels good" or "to push it to the max" can do too much damage to muscle tissue to be recovered easily, mitigating results.
So you give your body a strong signal to build muscle using progressive overload and big compound lifts, now the fun part - eating and sleeping. Ensuring sufficient protein intake (1 gram per kilogram of body weight per day is a good metric), sufficient sleep (at least 8 hrs, 10 is nice after a tough day), and a solid rest day after each workout day, all very important. Bear in mind also that the body burns what you feed it. Eat carbohydrates, burn carbohydrates - switching to fat burning metabolism will be delayed until after a bit of starving. Eating fat tells the body that it's fat burning time, so eat healthy fat and not in wild excess. Put these tricks together and great results can come quite easily - I converted 50 lbs of fat in less than as many days, went from 200+ to ~150 in around a month when I first brought my body online, back in 2003.
I know people get good results with ketosis, as would be expected, but in order to achieve lasting results, muscle building is absolutely necessary as muscle also adds a lot to your general energy requirements throughout the day. It takes a lot more energy to do all your basic stuff when you have more muscle tissue, so it's important to not just lose fat but also to gain muscle in correspondence unless you want to eat like a much smaller animal forever. I like cooking and I like eating so it's nice to be able to do so without concern for weight gain. There's definitely a critical mass that you encounter where it becomes impossible to gain weight with a regular eating routine as you have too much muscle to have any energy to spare unless you really deliberately eat for gaining, which is another adventure entirely. If you want to get on board, I highly recommend a thorough read through the Stronglifts 5x5 program which is quite wise and has yielded excellent results for me personally.
Heat is the next big energy use in the body. If you're wanting to do more mild maintenance or aren't ready to climb the mountain of strength and muscle growth, heat management is a reliable boat. Pay close attention to your metabolism and body temperature. The goal from this angle is to pop the temperature up at least 3 times a day, spaced out at intervals. This keeps the base metabolism from dropping into hibernation all day long. When doing long stints at the computer in film school with time constraints, I found a 10 minute round of solo footbag/hacky sack was a devastating method to achieve this end. Power jumps are another favorite of mine - go into a full squat, then jump for the ceiling with all your effort... 10 of those takes less than a minute and can be done anywhere, and I will be very surprised if you don't break a sweat. A handful of minutes of effort throughout the day in this fashion yields a much higher metabolism and core temperature inbetween, which burns a heckin' heckload of energy.
A couple other things to mention, never neglect your flexibility, pay close attention to your limitations, don't force the body if you're totally cold or far out of shape - get warm and get limber before you push hard.
Beware sitting. Sitting is one of the big dooms of modern lifestyle as it cuts circulation to the lower limbs and sex glands as well as completely reshaping the musculature of the back, legs and neck. It takes years, decades even to repair the damage from sitting at the PC through childhood and adolescence as I have realized, and there are far reaching effects on the shaping of the supporting musculature. If you must sit, pay close attention to your posture. Stand up and stretch regularly. Counteract it with activity as much as possible, lest ye pay the price in time.
Good luck in your journey!