We are just coming to the end of fitting our new kitchen. I have spent 12 months thinking about it and planning it, and everything is right for my space and how I work.
My advice would be to take your time planning it. The style of doors can be relatively easily changed, but locations of appliances and worktop space isn't as easy to alter.
Look on Houzz, in magazines, on the internet for ideas of styles of doors, clever storage ideas, and just things you haven't even thought about. The kitchen lessons learnt thread on here is great for ideas too.
Think very carefully about the layout, the Ikea software is good for tinkering about with unit positions, even if you don't buy an Ikea kitchen. Don't be afraid to ask a designer to re-design it if it will not work for you as everyone is different. If you're not very good at visualising it, use newspaper / masking tape on the ground to mark it all out full size and walk round it pretending to cook etc to check it will work for you.
Think about where you will put hot things out of the oven to check them? Where will you put hot pans if you need to take them off the hob? Where will you put your plates or serving dishes when dishing up a meal? Where will you put your dirty stuff before you load the dishwasher or if you need to run two loads (eg after a large meal, so a load for pans / cooking stuff and a load for plates, glasses and cutlery etc)? Will this be on show and will it irritate you while you're eating? Where will you put the toaster or kettle? Where will you use appliances that you don't keep out (eg blender, mixer, slow cooker etc?), will they be in the way of anything else such as where you dish up or where you put the food from the oven? Where will you prepare food? Can you fit people in doing different tasks, such as preparing a meal / cooking, making a hot drink, emptying the dishwasher etc without being in each other's way too much? Can you empty the dishwasher without having to close the door to access a storage cupboard for lots of the items? Think about where you are going to store everything - your everyday plates, granny's best china, cutlery, cooking utensils, herbs & spices etc, tin foil etc, bins, cups, glasses, bread, veg that doesn't need to be in the fridge, baking stuff, appliances that you don't want / need out all the time, roasting tins, the worlds largest turkey serving plate, wine, cooking alcohol, cook books, tea towels (in use and storage), kitchen paper, etc etc etc. everything needs a home, otherwise you will be cursing every time you need it or have to move it to reach something you use more often.
Think carefully about the lighting design, you will want focused task lighting in strategic locations and softer lighting that can be left on which is fine for making drinks etc at night.
I'm sure there are other things I thought about too, but they are the main ones. Hope that helps!