Your baby will be ready to expand his diet beyond breast milk or formula when she has reached some key developmental markers. Those usually include being able to sit up with support, holding her neck upright and steady, having good head control, and doubling her birth weight. You might notice that as your baby approaches 4 to 6 months she's more interested in reaching out and grabbing the food that you're eating. Since most babies lose the tongue-thrust reflex (when infants push their tongue against the roof of their mouth when a spoon is inserted) at about 4 months, you'll find it easier to spoon-feed her. The process might take awhile; introducing a variety of solid foods is a gradual process.

During your baby's first year, his menu will still include breast milk or formula before switching to cow's milk. The American Academy of Pediatrics recommends that babies be breast-fed exclusively for at least the first four months, preferably six months, and that breast-feeding continue until your child is 1 year old, even after you've introduced solid foods. Be sure to consult your own pediatrician about what to feed your baby, when to introduce solid foods, and how to introduce new foods.

Your baby's first solid food will probably be a mixture of a tablespoon or two of dry infant rice cereal combined with breast milk or formula. Assuming your baby doesn't have an allergic reaction to the cereal—rashes, repeated vomiting, diarrhea, or constant fussiness—after three to five days, you can gradually make the cereal thicker. Once your baby tolerates rice cereal, you can introduce other foods, one at a time, like oatmeal, barley, and wheat, as well as puréed fruit, vegetables, and meat that you buy in jars or make yourself, waiting two to three days before adding a new item. Once your baby is around 7 to 10 months old, you can introduce soft foods such as well-cooked pasta, bread, avocado, cheese, fruit, and meat that are cut up for easy chewing. Always supervise your child when he's eating. The AAP expressly states that small infants not be given raisins, nuts, popcorn, or pieces of hard food because they could be choking hazards.

Your pediatrician will be your best source of advice about what to feed your baby and when, as well as what to do if your child refuses to eat certain foods or starts to eat less (which is not unusual when a baby is teething or unwell). She'll probably give you lists of foods your baby can eat and tell you what to avoid (such as honey, until age 1, or peanut butter, which is usually off-limits until age 2). You might be told to introduce foods one at a time to make sure your baby isn't allergic to them.

What Food to Feed When

(Source from: http://www.consumerreports.org/cro/baby-food/buying-guide)