Think about where any restrictions lie: any item requiring plumbing (sink, dishwasher, washing machine) will need to be within easy access of the water in and outlet, any extractor fan needs to be on an outside wall, and try not to position the oven next to the fridge.
Think about how you want to use your kitchen: How much time will you be spending in your kitchen every day? Is it the focal point of your home? Will you be eating or entertaining in it? If so what seating will you have? Do you want to hide stuff away in it or put it on display? Do you also need it to store utility items (ironing board, vacuum cleaner)?
Imagine using your new kitchen. Go through the process of making a cup of tea: where do you store the cups, where’s the water, the tea bags, the milk, the waste bin? Do you have enough work surface for food preparation, serving, storage?
Consider where you will put portable items such as microwave, kettle, toaster and music station or TV.
Lastly, think about lighting (ceiling, wall or low level) and heating (under-floor, plinth heater).