(Unabashedly lifting thoughts from Robert A. Heinlein...)
Let's have citizens granted the right to vote only after they've served
their country in some fashion for a minimum of two years.
If you don't want to serve, you still get all the other benefits of
citizenship -- you just don't get a chance to vote yourself bread and circuses.
Please read Starship Troopers by Heinlein if you need more information
about the pros and cons of this suggestion.