I just came back to post the same thing Lizzie.
Obviously when planning you have to take into account the shape of your room, position of windows and doors and where the external walls are.
In our kitchen, following all the regulations (water away from electricity and so on) points were
1 Keep equipment away from doors or thoroughfares for safety reasons
2 Plenty of clear space either side of the hob and oven
3 Position fridge and place to make hot drinks, toast etc. away from the main cooking area so that people coming to get drinks if I'm cooking, are out of my way and it doesn't get congested
4 Position of dishwasher and crockery cupboards the same principle, so people don't get in each others way
5 A deep larder cupboard which gives loads of storage
6 Bookshelves for cookery books, radio and stuff like that
Most of the time we keep the island unit clear with just a plant, vase of flowers or bowl of fruit on it, but I do use it for prep work sometimes too and it cleans down easily
If there's nowhere else, you also need to think of where the ironing board, mop, vacuum cleaner and that kind of thing are going to live.
Have a look at some sample layouts that would fit your room and try and imagine yourself cooking and spending time in there. Get a feel for it.