This is a good subject, but sadly there’s no a good topic, or better, a wiki page that would summarize all information about rendering with Synfig. D.j.a.y posted a “call for writer” some time ago, but no one wants/able to step into and thus we still don’t have a wiki page about it 
I can only share my own knowledges about it (and they’re poor):
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Don’t set “Quality” parameter less than 3 (default). You likely won’t notice any difference in video quality, but rendering process will be increased.
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Don’t set “Anti-Aliasing” parameter greater than 1. Rendering time will be increased significally, but effect on quality will be highly noticeable.
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Don’t set “Frames per seconds” greater than 24. You only need to set it greater if your scene involves many moving objects (the scene is very dynamic).
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If you use Windows it’s better to render your animation using “Target” set to ffmpeg and “Parameters -> Available video codecs” set to “Windows Media Video 8”. Then you can use “Movie Maker” to edit your animation. It’s free video editor from Microsoft. Average functionality, but interface is user-friendly and simple.