Perhaps an obvious, but not often considered idea is that you are designing a kitchen for your home, make it size appropriate. Consider the type of cooking you will be doing on a regular basis. If cooking isn't your thing then an intimate design where everything is handy may be just right for your home. On the other hand, if you have four kids, entertain half the neighborhood, and invite all the relatives for holidays, you may have need of larger appliances and work spaces.
Ask yourself if there is one person who does most of the cooking, or if it is a family activity. Consider what the kitchen will be used for: is it only for cooking, or is it a place where people hang out? You may only eat casual meals there, or perhaps it is the central gathering point for your whole family.
Good kitchen design still focuses on the basic triangle of stove, refrigerator and sink with 4 to 8 feet between units. But if you plan to have more than one person working in your kitchen, think of multiple triangles. An island work station with a prep sink, or dedicated spaces- perhaps for baking, or a desk / recipe storage area may help. Use plenty of lighting, and consider putting the sink in a center island if you don't have a nice view for that traditional over-the-sink window.
There are few things more bothersome in a kitchen with too little counter space, or cabinets that don't provide the kind of storage you need.
Pay attention to corners. Poor design makes them difficult to access or too dark to be useful. Cabinets with lazy susans or blind base pullouts can help. Think carefully about the sizes of the doors and the directions the doors and drawers will open or you may end up with years of annoyance. Consider whether you want the convenience of pull-out shelves in your base cabinets, or the extra storage you'll have on regular shelves.
Stock cabinets are the kind that you can choose and take right home from the store. Most everyone can use at least some of these standard sizes. Semi-custom cabinets are built after you place your order in sizes to fit your particular spaces. These cost a little more, but will give you more flexibility in creating storage that is perfect for your kitchen.
Custom cabinetry is made by hand so that each component is built exactly to your specifications. These are the most expensive, and take longer, but will allow you to make the best use of your space.
Specialty inserts, trays or racks can make your cabinets serve in particular ways.
And don't forget about finishes and hardware. The same cabinets can look quite different with light or dark color finishes. Even a change in hardware can change a look from casual to formal or bold.
Plan carefully and you'll enjoy your kitchen for many years.