Diets only work in the short term. This is because whenever we go 'on' a diet', our subconscious mind automatically stores the question: 'when are we coming OFF the diet?' So diets do nothing to change our attitudes towards food and eating. Eventually, after the novelty of eating perfectly wears off, reality kicks in and we realise the motivation just cannot last.
Whatever eating plan you choose, it must be do-able long term. That means you need to allow yourself some times where you get to eat some of the things you love without going overboard. If you do the right thing most of the time, you will lose weight and you will keep it off.
Whatever you choose to do, whether it be an eating or exercise plan (or both), ask yourself the question: 'Do I see myself doing this for the rest of my life?' That will give you an indication about whether you are on the right track. Give yourself too much leeway and you'll gain weight or stay the same. Deprive yourself too much and after the novelty of the 'diet' wears off (usually in 2-3 months) you'll be climbing the walls and will probably end up bingeing.
When we get stuck in 'diet' mentality, we are on a rollercoaster and the ride is bumpy - we go from being 'good', then plummet to being 'bad'. Each time we fail we not only mess around with our metabolism, but our self esteem plummets as well.....and we re-affirm a belief in the subconscious mind that says 'I am a failure. I never finish what I start.' Since our beliefs create our reality we continue todo what we don't waint to do: fail.
The most important advice I can give you is to get off the rollercoaster.