Eat home cooked food. Unless you know exactly how a certain restaurant runs, try to eat more home cooked food as that is generally more environment friendly. But if eating out, get leftovers home.
Plan your meals. Plan meals in advance and make shopping lists for ingredients. Plan meals around products at home that are near expiration dates or wilting or going stale or over ripe. Designate a meal a week as a use-it-up meal from what's left in the fridge/freezer/cupboard.
Shop well. Buy exactly what you need. Don't be afraid to buy ugly or funny looking produce to avoid these going to waste - there are also many websites now that sell imperfect looking produce.
Move older products to the front in the fridge/freezer/cupboard. Store dry produce in air tight containers.
Make sure the fridge is running at the right temperature. Store food in the right place in the fridge & freezer. Some foods are better outside the fridge - like bread, banana, pineapple, potato, onion, tomato, garlic, cucumber.
Foods that produce ethylene gas (banana, avocado, tomato, cantaloupe, peach, pear, green onion) should be kept away from ethylene-sensitive foods (potato, apple, leafy greens, berries, pepper) to avoid spoilage.
Keep the stems of vegetables like broccoli, celery & asparagus in water to keep them fresh.
Many dairy products can be frozen.
Keep serving sizes in check. Take small servings to avoid waste. If eating out, split a dish with friends or family.
Compleat food. See ways of eating the entire food so not letting any edible parts go waste.
If there is still unused food, put it to good use. Make a face/hair/eye mask from ingredients like overripe avocado, used coffee grounds or used tea bags. Donate unused food (including scraps which farmers can take for animal feed) through apps like OLIO or compost it. Monitor what you throw away so you can take some action.