Cook several main dishes when you have more time like on a weekend. Make soups, stews, or casseroles to freeze for the next week. Cook extra food as "plan-overs" for later use.
Do some tasks ahead. Wash and trim vegetables, cook noodles for a pasta salad or cook ground meat for tacos a few hours ahead or the day before you need them. This can save you lots of time during busy weekday evenings. Always refrigerate cut vegetables and cooked food right away.