I started on solids when my son turned 5mths, just with rice cereals at first and I added pureed pumpkin to it after a week. Rice cereal is supposed to be a good starting food since it can be easily digested and most of them are fortified with iron as iron starts to deplete when they are 5-6mths old and hence you need to increase their iron intake.
It helps to make a big batch and freeze in small portions and just take out whatever you need everyday (call me lazy, I make rice cereal in bulk as well!). I have a lot of fun feeding the baby, but, it does get messy, really really messy..........