lessons learned (never again!)
corner units and drawers are expensive and so what your designer will try to sell you. Pan drawers are good. Internal fittings are not needed.
no internal carousels etc - eat up space and break. And cost lots.
no integrated appliances except the oven - the extra door on the front makes for extra weight, integrated items are always pricier and have less internal space. HOWEVER make sure your kitchen designer leaves at least a 64cm space for a 60cm wide appliance and notices if there is a skirting board. (guess what happened to us?) Buy your appliances from Currys/AO etc not the kitchen supplier.
check the design for pointless end panels, cost money, waste space, do nothing. Get them all removed and keep checking as they sneak back at each revision. (wish we'd noticed this)
check that the designer has measured the room correctly. (Guess what happened to us?)
have a space for a normal bin/recycling container. Put a bin in a cupboard and it is an extra door to open. Don't have a tea towel rail in a cupboard, they never dry and you have to open the door with wet hands. (this is a really stupid thing)
handles should not have any sticky-out bits to catch on clothing.
if you have a gas hob you can't have a glass splashback, the worktop won't be deep enough. Use tiles. If you have another type of hob and want a glass splashback, buy online for about £80 rather than paying £300 plus from a kitchen designer. Still make sure the worktop is deep enough.
Tiles are a lot cheaper than upstands, especially if you can fit yourself. Make sure sockets are placed high enough up to clear upstands or tiles.
A kitchen fitter should only fit a kitchen. Make sure there is a separate plumber, plasterer, floor layer, electrician and gas engineer (if needed). Do not let kitchen fitter do plumbing or floor screeding as he will cock it up even if he thinks he can do it.
laminate worktops unless you are made of money (posh stone stuff) or like doing lots of work (wood).
extractor fan not silly ugly noisy hood. Straight run to an outside wall if at all possible.
good luck...