Invites should be memorable, distinctive and reflect your personality. Off the shelf invitations are generally not this.
When thinking about your text - keep it simple!
example of simple text
Keep fonts to a minimum - 2 styles is better than lots of different ones, any more makes them difficult to read. Complicated typographic layouts will almost always detract from the message.
example of complicated text
It's generally recommended to keep invitations to 10-14 lines of copy. Centering the copy makes it easier to read, as we tend to read them on a line-by-line basis.