Is Baby Ready for Solid Food? Signs of being ready for solid foods at wholesomebabyfood.com):
Loss of tongue-thrust reflex - This allows baby to drink and swallow liquids with ease; with the tongue-thrust reflex still present, baby may simply drink in liquid purees or push the food back out. According to Dr. Jim Sears, in the first four months the tongue thrust reflex protects the infant against choking. When any unusual substance is placed on the tongue, it automatically protrudes outward rather than back. Between four and six months this reflex gradually diminishes, giving the glob of cereal a fighting chance of making it from the tongue to the tummy
Ability to let you know she is full from a "meal" with signs such as turning away from the bottle or breast. This is important so that baby is able to self-regulate the amount of food being eaten. This helps stop baby from accidentally overeating as parents may continue to feed baby thinking that she is still hungry.
Ability to sit up and hold head up unassisted
Interest in your food (we tend to disagree with this one as when a baby reaches the age of 4-6 months, he is interested in putting everything in his mouth.)
Doubling of birth weight
Frequently waking in the middle of the night when a solid sleeping pattern had been established. This may not be the best indicator that your baby is ready for solids. Please keep in mind that a growth spurt will occur between 3-4 months of age, 6-7 months of age and also 9-10 months of age. Baby may also be waking due to an illness or teething.
You can refer to www.wholesomebabyfood.com for more information about feeding baby. It's a very informative website.
For my dear daughter, i started her on a bit of Heinz rice cereal at about 51/2mths. From 6mths onwards, i started her on barley, oatmeal and brown rice cereal from Healthy Times. She also had some Moon Rabbit Si Sen brown rice gruel for awhile. After making sure that baby's not allergic to the cereal, you can start introducing vegetable and fruit purees. Make sure you follow the 4-day wait rule (dont't intro more than 1 new food at a time, wait for 3-4days to see if baby has an allergic reaction to the new food). When you've established that your baby's not allergic to the veg/fruit puree, you can add the puree to the cereal or you may wish to continue to feed them separately.
The url i gave you has a comprehensive guide to what to feed baby and when.