Use creative (dollar store) visual aids. Add Animation!
At the appropriate part of the Haggadah throw out toy frogs... cows and animals... snakes and spiders (beware)... ping pong balls (hail)... wear dark sunglasses to simulate darkness...
Prominently introduce (with a vocal drum roll), honor or reward the child asking the Four Questions, good readers or singers, or any good question raised during the Seder.
We read the Haggadah in a language we understand, but its interesting to also hear a paragraph in a foreign language.
Share the wealth! Go around the table and take turns reading the Haggadah.
Assign topics of discussion, such as the The Four Sons and ask a guest to prepare and present each son.
Theres no dumb question. Encourage all ages to ask, and invite everyone to think of possible answers. Prepare questions such as: The Haggadah states that this year we are still slaves and not free. What is the Jewish definition of freedom?
Next year in Jerusalem?
How many really want to live in Israel? What does Jerusalem mean to you?
Whats wise about the wise son? What defines wisdom?
The Seder is not a dinner party. Advise your guests to eat a little before, so they won't be starved to rush through the Haggadah.
Use the same Haggadahs so everyone can follow along. There are also kid's versions. On the other hand, a unique, exotic Haggadah makes a good conversation piece.
Check out Chabad.org before Passover for great tips and insights to enhance your Seder. It's also a good source of general ideas to stimulate conversation.