It's important to choose a formula that is iron-fortified. Low-iron formulas are available due to the belief that iron makes babies gassy and constipated, but studies have found this to be untrue. If there's a family history of allergies, you believe your baby is lactose intolerant, or you have other health concerns, consult your pediatrician--he or she can steer you toward the formula best suited for your child's needs. Most formulas come in a powder or concentrate form (both of which you mix with water) or ready-to-feed form (the most convenient -- and expensive -- option).
To feed your baby, cradle her in a semi-upright position and support her head. Don't feed her lying down -- formula can flow into the middle ear, causing an infection. To prevent your baby from swallowing air as she sucks, tilt the bottle so that the formula fills the neck of the bottle and covers the nipple.
Your newborn will probably take between 2 and 4 ounces per feeding during his first few weeks (during the first few days, he may take less than an ounce at feedings), and will probably be hungry every two to four hours. Use this time frame as a guide only. It's best to feed your baby on demand. Don't encourage your baby to finish the bottle if he's not interested. And if he's still sucking enthusiastically when the bottle is empty, offer him more.