Ok Folks, here is a comprehensive guide to improving your nutrition and feeling better/potentially helping you trim a bit of fat if that's your thing.
I'm going to present it as a series of suggestions, @Nutcuttlit will add to this list also as he has expertise here too.
1) The best way to feel good is to get the appropriate amount of vitamins and minerals. These come from good quality food and a varied diet (more on this later), my first suggestion is really simple. Go to amazon and buy yourself a Vitamin D and a Vitamin B tablet - these are two essential vitamins that EVERYONE lacks in their diet. Here is a link to the ones I would suggest: Vitamin D Vitamin B These pills have exactly the correct amount you need per day.
2) Changing your eating habits is hard, it takes 21 days for something to form as concrete habit. My second suggestion is to make 1 change a week, this will make it easier to sustain and turn into a new habit. My biggest suggestion for a change right off the bat is to take a healthy lunch with you to work, I have grown very fond of my Thermos Compartment Flask as it allows me to take a hot lunch in one side and some carrots, cherry toms, cucumber in the other. It also has a spoon in it, it's all encompassing. This way I know I have a tasty lunch I WANT to eat and my obligatory veggies that will keep me full.
3) Losing weight is rather easy, its just the application that difficult. My final suggestion is to keep a food diary. Download MyFitnessPal (it's free) and scan/log EVERYTHING you eat. Once you know how many calories you're eating daily (just be honest when you track, no one is gonna know except you), all you have to do is remove some of the calories to start losing weight. A good deficit is about 500kcal a day, however this doesn't have to be from just your food. You could try and burn 300kcals exercising (walk up and down the stairs for 20mins - that's the easiest 300kcals you will ever burn) and then ditch 200kcals from your diet.
This should be enough to get you started, I'm going to add a meal planner thing later today!