Here are some questions to ask yourself when considering learning Revit:
1. How well do I know how buildings are constructed?
2. Do I have any experience with CAD in general?
3. Do I have Microsoft Windows experience?
If you said yes to the previous questions consider this path:
1. Do the "Getting Started" tutorials under the Revit Help menu.
2. Take minimum 4 days of instructor lead fundamentals training.
3. Register with http://www.augi.com/ where hundreds of architects discuss Revit issues.
4. Start a project ASAP! You won't be disappointed.
Within 3 months you will be comfortable and starting to gain some serious productivity. If you don't take training it could take up to 6 months.