This is copied and pasted from what I wrote in Jacey's thread on weight gain, hope some of it helps, I will warn you now it's a mega essay and a half lol, but it gives you some good info so you don't get bored of peanut butter on toast every morning
Put quite simply you need to eat more calories than you use - and you need to do this regularly. It's not enough just to have occasional extra snacks.
Set yourself a realistic target weight and aim to increase your weight gradually, by about 1 kg (2 lbs) every month until you reach it. To do this, you'll need to take in about 350 extra calories each day. Your body will respond better if you do this by eating healthily, rather than just eating more chocolate or fatty foods.
It's important to eat regularly throughout the day. Plan to eat 5-6 small meals, plus two or three snacks in between. If you find this difficult at first, you could start with smaller meals and gradually make them larger. To add more calories to your meals, you could:
* have an extra slice of toast for breakfast,
* drink grape juice rather than orange or apple juice,
* make coffee and tea with milk,
* serve an extra spoon of mashed potato, wholemeal rice or wholemeal pasta,
* add lean minced meat, lentils, beans or noodles to meals like casseroles and soups,
* be more generous with healthier unsaturated oils, such as olive, sunflower and vegetable oils, salad dressing and spreads, and
* always have a dessert.
Using fortified whole milk in your hot drinks will also add more calories (you can find this with the UHT milk in the supermarket), but try and cut down the amount of tea and coffee you drink each day, replacing it with milky drinks instead.
To help you keep on track for your target weight, it might help to keep a food diary
As well as eating regularly, it's important to eat healthily. Your diet will be balanced if you eat foods from the five main food groups in the right amounts.
* Carbohydrates like bread, pasta and potatoes should make up about one third of your diet.
* You should aim to eat at least five portions of fruit and vegetables each day.
* About one fifth of what you eat each day should be protein - choose from meat, fish and eggs, or beans and nuts.
* You should aim to get 700mg of calcium each day, roughly the same as a pint of milk or two small yoghurts. You can also get calcium from soya milk and yoghurts with added calcium, and from leafy green vegetables.
* Fatty or sugary foods like butter, chocolate, crisps and cakes should make up the smallest part of your diet.
Keep some healthy snacks handy, to make it easier to keep to your plan. You might like to choose from:
* fresh or dried fruit,
* cereal or cereal bars,
* milk, yoghurt drinks or smoothies,
* flapjacks, scones or fruit buns,
* nuts and seeds,
* pots of rice pudding, custard or yoghurt,
* wheatmeal biscuits,
* pasteurised cheese and crackers.
And, of course, a small chocolate bar once in a while doesn't do any harm!
Ideas for more filling snacks include omelettes with healthy fillings such as ham, cheese or mushroom, baked beans on wholemeal toast, and jacket potatoes with toppings like tuna and coleslaw or cold chicken and turkey.
