I wouldn't be able to handle "being on a diet" and restricting myself every day. I have generally decent habits (shame about Christmas and Easter) and can handle 5:2 with an isolated day at a time and defer what I desire until the next day, by which point the feeling has passed. Much easier than a long term sense of deprivation which can lead to a rebound binge. Life happens which is where I sneak a pound here and a pound there, so I'm using the 5:2 to compensate for those occasions and phases where I consume more than I burn.
My Fitness Pal is a great app. The hard bit is being ruthlessly honest, not letting a bit of this slip past and getting the portion size right. It's a good tool to assess what you are actually taking in and seeing what you can reasonably adjust (food choice, portion size). It is helpful to think of food in terms of its nutritional content. Is a meal balanced. Is the fat content of the avocado better than the donut. Has a meal got a range of protein, carbs and veg?
Exercise is great for boosting metabolism and feeling good. It buys some extra calories, but not that many. It grieves me that a pack of mince pies is the same calories as a Half Marathon, because it does not take me over two hours to scoff 6 mince pies
It does however on average boost me by a couple of hundred valuable calories per day (which being a short food lover really matters!
Assess your current habits. What is good, what needs tweaking? Over time, amend them, reduce portions, be more selective. It can be done without a "diet" but it will need a lot of patience, but that way the results will last.
People that do make the difference long term are those who change habits and don't feel deprived along the way. It can be done 