We've started out with just simple subjects and predicates. Better known as the noun and verb I suppose. My son hated to just diagram his Eng. book sentences so I dug out the words we had used for the Montessori farm, and they worked perfect.
I even found a little fishing tackle box to fit them in nice and neat. :) I tell my son how many sentences he should write on his paper, and he builds them, diagrams them, and then writes them on his paper. :) It made all the difference just being able to make up his own sentences.