There is no single right way to plot, so it's best to research different methods, try them out, and keep what works for you. To get you started, here are
Ten Things to Help With Novel Plotting
1. James Scott Bell's Structure Secrets.
2. Stella Cameron's Plotting Your Novel.
4. Jeff Heisler's Plotting.
5. Randall Ingermanson's Snowflake Process.
6. Holly Lisle's Notecarding: Plotting Under Pressure.
7. Lee Masterson's Plotting Your Novel.
8. M. Mulgrew's Plot Outline Diagram.
9. David Sheppard's Plotting.
10. S.L. Viehl's Single Novel Plotting Template.*
*I haven't updated the copyright note at the bottom of this, but my plotting templates are free for anyone's personal use or non-profit distribution. If you do post or reproduce the template, just remember to give me the byline credit.
(Links updated 2/14/09)