You've picked the precious stone and metal. Now, it's time to choose a design. You don't have to come up with one out of thin air. Visit jewelry stores to peruse different styles. Check out the latest trends in wedding magazines. Consult a professional jeweler. If you're thinking less contemporary-chic and more timeless-classic, find inspiration from your favorite historical era or architectural style. Remember, you're creating this ring, so nothing is off-limits. Art Deco, Victorian and Byzantine-inspired bands are all new again with your signature take on the aesthetic. Retro styles, geometric designs, etched engravings -- it's all possible.
Even if you're on a tight budget, you can still draw inspiration from ritzy rings. Incorporate elements you like into your own design. You can't have the knuckle-sized diamond, but that filigree and intricate latticework? No problem!
One thing to stay away from? Fads. You'll probably be keeping this ring for the rest of your life, so go with a design that won't feel dated in a few years. Choosing an engagement ring based on its current popularity would be like getting a tattoo memorializing your Twitter user name. It might make sense right now, but in a decade or two, its relevance will have waned, and it'll just be embarrassing.