Stop eating out regularly - and If I'm eating out, share half portions with my partner. (Some restaurant meals include an entire adult's calorie allowance in one sitting.)

Stop buying takeouts (ditto.)

Stop eating sandwiches, or any food with concentrated carbs, because they're high in calories but very unfilling.

Eliminate foods that cause cravings (e.g. certain milk chocolate bars, which apparently increase appetite for hours afterwards.)

Pay attention to food effects, and avoid bad foods - i.e. high calories, unfilling, cravings - because to some extent the foods that cause these effects are personal.

They're also age dependent. (You can eat a lot more in your 20s than your 50s.)

All sweet and sugary food is bad. Avoid. No exceptions.

Bulk out meals with salad and/or eat soups with plenty of water content. (The water/fibre suppresses appetite.)

Go for an hour's energetic walk every day, including a few uphill sections. (Pokemon Go works for this.)

It's a fairly gentle and informal regime based on simple rules and diet changes rather than obsessive monitoring and exercising. But it lost me over 10kg over a few months.