Spend as much as you can on worktop. The cupboards are standard and worth next to nothing, it's the doors on the cupboards you pay for, but the worktop is used daily. (remember real wood worktops MUST be oiled to maintain them and granite WILL stain and require fine sanding and polishing to get rid of stains)
Be careful choosing handles as some of them should only be used on wood and not MDF etc (check what your cupboard doors are made of eg. 16mm MDF, 18mm MDF, soild wood with MDF panels)
If choosing a 'no handle' type of door, you'll need to be able to adjust the door hinges yourself (it's easy), as all doors subtly move out of alignment with use, it's just REALLY noticeable in the 'clean lines' of these doors.
Get quotes yourself from different places and haggle. If you time it right with sales etc, you can actually haggle a LOT. E.g Howdens sale is Oct EVERY year, and they'll give you a 'normal' quote and an 'oct' quote, which will have anything up to 40% off, you can then compare with B&Q/ Kitchens direct/ joiner quote etc and haggle them ALL down. This works with whichever place currently has a 'sale' on.
Your 'wall/ base/ tower ends as well as cornice and pelmets actually make the kitchen look well finished, so make sure you use them, there's nothing worse than a lovely new kitchen has the white/ oak of the basic bare cabinet visible, cos it makes it look cheap. ( Joiners will get your kitchen design pictures WITH cornice/ pelmets /ends and lighting, get you to pay for it, then take them off the bill before paying for it, thereby pocketing the cash and telling you you'd need to pay extra for these). So ask for an itemised invoice BEFORE you pay, and make sure. ( ALL the places that give joiners a trade discount give them an itemised invoice, then ask for a non itemised one to show their customer, usually with a couple of grand added which is taken off again before they pay). So if you can get an account yourself, do it.
Doesn't matter where you want the sink/ hob etc, just make sure your 'working triangle'( i.e fridge, cooker, sink) is as small as possible as this is what actually makes a kitchen 'user friendly' (as any designer will tell you).
Don't put tower units next to your windows as they really do cut out a lot of light.
If you choose a 'coloured' sink and tap, be aware they do NOT keep their colour (sunlight bleaches them, food stains mark them etc and the colour often peels off the taps in time).
Take your time choosing and comparing, remembering to check online retailers for cheaper appliances/ sinks/ taps/ lighting/ etc.