I love the baby's "first food" stage. I don't worry about greens because they are getting mostly breast milk at this stage - which essentially is green food, in so many ways. So I stick to soft fruits and veggies and what ever is in season. Legumes work too, but maybe introduce those later, at like 10 months.
I get really excited to get creative and see what kinds of fun things I can get the babes to swallow (my favorite part is seeing their faces upon first taste). RIPE foods are the key! Make sure they are mashable and/or something the child won't choke on.
I normally stick to raw foods like bananas and papayas and later on maybe some sliced grapes. NO citrus or berries just yet (too acidic for their digestive systems). I learned the hard way last year when my other son chowed down a strawberry. HE LOVED IT and made the best faces. But he threw it up in the middle of the night. I found him the next morning with crusty, puke smelling strawberry "sauce" all over his hair and pajamas.
Baked apples are obviously GREAT and very popular. But if you have a Vitamix, you can blend raw apples to a smooth consistency without having to cook them. (yet another reason to get a Vitamix.)
Try juicing apples and then adding that to the raw apples and BLEND AWAY! Or use breast milk or just purified water. I always like to add some omega-3 (like flax with DHA) oils as well!!
Also, stick to just one food before mixing them. Mix them later on after his/her digestive system is used to food.
Sweet potatoes and brown rice are fun to fill them up but the starchier the foods the fuller and the "fatter" they will get.
Boiled squash is a great one for the winter time (again mash with flax oil).
Some people wait until the child can sit up and pick food up with fingers before they feed them. I like to start when the baby seems to be "hungrier" than normal anytime after 6 months. I don't feed them very much, just sort of an appetizer type thing, to warm them up to the idea of spoons and finger foods.
We just got a new high chair and I am SO excited to start using it!
NOTE: In case you're looking for more information from pediatric type authors (as opposed to myself) I found this article on the La Leche League web site. It's pretty basic and informative.