Here are some suggestions to avoid rendering:
Edit the majority of your project using cuts only; add only transitions, effects, or filters that can play back in real time or that are absolutely necessary in making decisions about your first cut. Avoiding unnecessary effects and time-consuming rendering can help you focus on your program’s overall pacing and structure. Once your first cut is done, you can focus on applying effects like color correction and titles.
Use the Unlimited RT mode and dynamic real-time playback. For more information, see Using RT Extreme.
If you use effects that need to be rendered, you can get a good idea of how the clip looks by simply scrubbing through the clip in the Timeline or Canvas to view the effect one frame at a time.
You can also choose Mark > Play > Every Frame (or press Option-\) to play through a clip one frame at a time, not in real time, and get a slow-motion preview of how the effect will look.
When you change the In and Out points of a clip with filters applied, you may need to rerender the adjusted areas. To avoid constantly rerendering, you can place a clip with its applied filters into a sequence and then edit that sequence into other sequences. This is sometimes called nesting a sequence. Because you modify the sequence In and Out points instead of the clip within the sequence, the render file for the clip is maintained. For detailed information about nesting clips using the Nest Items command, see Sequence-to-Sequence Editing.
Turn off filters that require rendering when you don’t need to view the effects in order to make decisions.
Turn off the rendering and playback of filters, frame blending, and motion blur individually. You can also turn off filters and frame blending collectively in the Render Control tab of the Sequence Settings window. These options can be turned on at any time.
Temporarily turn off rendering of clips that cannot play back in real time. This allows you to make changes to effects-intensive sequences without having to wait for frames at the position of the playhead to render for display in the Viewer or Canvas. For more information, see Temporarily Disabling Rendering.
Here are some tips for reducing the amount of time it takes to render your sequence:
Lower the frame rate and resolution of rendered effects in the Render Control tab of the Sequence Settings window. This lowers the playback quality of those effects but allows them to render substantially faster.
Turn off certain render-intensive effects in your sequence, including filters and frame blending. Using the options in the Render Control tab of the Sequence Settings window, you can turn all such effects on and off in your sequence without having to turn on or turn off each effect individually.
Test-render short sections to evaluate an effect, rather than the entire clip or sequence. You can always begin rendering a clip and then stop the render midway. Final Cut Pro preserves what was rendered, so you can see how it looks without having to rerender the entire clip.
Render sequences while you take a break or do other work by turning on automatic rendering in the General tab of the User Preferences window.
In this case, rendering time isn’t actually reduced, but you can make efficient use of your time by turning your attention to other things as the computer renders your media. For more information about the Auto Render option in the General tab of the User Preferences window, see Choosing Settings and Preferences.