First off, don't add the settler to your city until you've finished improving your land. Oops, too late
Remember that tip for next game then. Actually, you might want to build a settler at this point to keep improving your land. Depends on how close you can get to size 21 with your curretn set of improvements.
If you haven't changed to Republic, do so now (or research towards that goal).
If you don't have three trade routes established, do so now.
Build a colosseum, and the aqueduct, and celebrate WLTCD up to size 12. If you don't have enough food squares available to do this, research seafaring and build a harbour.
When you are size 12, you will find you still need to keep luxuries at 10-20%.
Your next goal is to build Shakespeare's Theatre. This is the part of the game that often drags a bit, as you have just spent most of your money/food caravans to build Copernicus. So don't don't be discouraged by taking 15-20 turns to get Shakespeare's Theatre. Yuo should be researching sanitation at this time too.
When you have Shakespeare's Theatre, sell your colosseum and temple, and build the sewer system. Crank up the luxuries to 30-40%, and celebrate WLTCD up to size 21 (if possible).
At this point, you will be advancing every 3-4 turns, and are well on your way to a successful game. Be sure to give all your science to the AIs, or the research rate will begin to drag.
edit: Don't build Isaac Newton's College before Shakespeare's Theatre. Getting up to size 21 quickly is much more important (and you need shakespeare's to do that. You will find otherwise that WLTCDs only get you to size 13 with a temple and colosseum, no matter what you set luxuries to.
[This message has been edited by Tom DeMille (edited May 05, 2000).]