Well, I had no idea myself... so, here's what I am doing. My doctor gave my a chart and it says that grains can be introduced at 3-6 months, veggies at 4-7, fruits at 6-9 so... I made up my own introduction sequence.
Introduced rice cereal for 10 days.
Sweet potatoe for 4 days... moved it to the dinner feed on day 5
Introduced apples... currently on day 5 tomorrow.
Introduced peas today.
What I plan to do is move through the introduction of foods in a cycle. Next food to be introduced will be pears.
Basically, I am doing...
GRAIN
VEGGIE
FRUIT
VEGGIE
FRUIT
I chose to do this because there are more veggies and fruit to get through than grains. I only plan to do rice, barley and oats right now. She will get wheat after 12 months of age.
I always introduce the food on its own. Then on subsequent days, I mix it with cereal.