Basics of kitchen design are work triangle, appropriate storage close to work areas and then aesthetics.
Work triangle is the positioning of sink, cooker and fridge to keep distance needing to be walked between all three as short as possible.
Appropriate storage is cupboard space for pots/pans, knives, spices/seasonings ( as mentioned above- spices away from heat, also wine racks they seem to get put next to the oven as a space filler too often).
Dishwasher next to the sink is always good, less plumbing required, sinks also come with 2 & a 1/2 bowls to multi-task but the option of a secondary sink near to veg storage is a good one if space allows.
Take note of the stature of the clients, tall or high wall cabinets are pain in the backside for vertically challenged people, just ask my Suzy [wink]
When you go to do a survey measure everything and note where all existing plumbing or electrical points are, moving some is no big deal but the cost of re-routing them all to suit the design gets pricey fast.
Some of the gadgetry is vastly overrated and accordingly overpriced, keep it simple but classy. The only things not overrated are full extension drawer slides, those things rock!
Rob.