You can either send out invitations, or bring them to each neighbors house. Make sure you don't exlude anyone from an invitation, as this can often create unwanted tension between neighbors.
The easiest way to get people to come to a block party (I just did it) is to go door to door and ask them! This way if you haven't met them yet, you will and they will at least know you at the party. Also you can talk about when they should bring!
