Depends
1: If you set the 1200 up to output a VGA screen mode (DBL PAL or Productivity should work), you just need an adapter for the monitor cable. (RGB to VGA or some such). Those are a couple bucks from amigakit.
This works great for workbench and a few (very few) games.
2: If you want to play games etc, you need either a scan doubler (indivision or an external box) or an LCD that supports the amiga screen modes.
edit: If you are in europe, and have an LCD with scart, you can get scart adapters and you'll be all set. Damn NTSC standard