The first thing we need to do is talk about what you want. If you haven't already, I suggest that you browse stock house plans, listed online on various home plan websites, to see if there's anything that's close to what you'd want. Then, answer these questions:
1) Do you want a 1 story or 2? (if a 2 story - do you want the master bedroom up or down)
2) How many bedrooms do you need?
3) How many full bathrooms?
4) How many half baths?
5) Do you want a study/home office?
6) Do you want a formal dining room?
7) How many living areas? (media/home theatre/game room/cabana)
8) Garage Size? (how many cars - 2, 3, 4...)
9) Primary ceiling height? (8', 9', 10')
10) What's the minimum and maximum square footage of the house? (give me a range)
11) What style of architecture do you like on the exterior? (search homes online and save pics that represent the exterior design style you'd like)
12) Do you have a sample of a floor plan that's similar to what you want?
13) What size is your lot? If you have a survey/plat, this is important to determine the maximum footprint of the house you can build.
14) Is your lot within a development with an existing HOA with current deed restrictions that define the style, size and features that are acceptable for the neighborhood?
15) What's your budget to actually build the house? This will ultimately limit the home size, exterior detail/character, design features, etc...
IMPORTANT: Before getting started with your home design, it's important to already own the lot that you are going to build on. This will save you a lot of time and heartache from designing a home that ultimately will not fit on the lot where you end up building.