The thing is, there is no diet required. A diet is nutrition for sick people. What most people need is a more healthy relationship to what they eat. Realizing the discrepancy between what your body needs vs. what you consume on a daily basis is a huge help. Initially I suggest to track their calories for a few weeks and then adjust your intake to serve your specific goals. After a few months you will have great intuition about the things you eat on a regular basis and don't need to track anything.
Weight is a simple game, if you want to loose weight, consume less calories than you burn. Do this over a long time and you will see progress. You always want to play the long-term game, so if you go out for dinner once in a while, enjoy yourself and don't agonize over your "diet". The progress is made in the little things you eat every day, not during a nice evening with friends.
Also, don't banish any macro nutrients, this will make your everyday nutrition harder. Eat lots of greens, some meat and fish, fruits, rice, pasta and potatoes, and an occasional donut or pizza.