I would like to hear it from you what is your animation process. So do you firstly sketch on a piece of paper and import it to Synfig? Or do you create vector graphics in Inkscape and than import it into Synfig?
Please tell what did you find best and suits you best?
I create Vector in Inkscape and then import it in Synfig. I also sometimes draw shapes which will be used for masking. I am not good with drawing on paper but vector graphics helped me.
You may find other methods easy and useful, @KEgg creates illustration (artwork/vector) and animation in Synfig. According to him it is a non destructive way of creating your artwork.
I usually use the sketch tool inside Synfig, then draw the vectorial shapes on top of that. I use to do backgrounds in Inkscape but some imports where problematic. I never had problems with importing images.
What I realized is that, you can decide what works best for you, you could even use synfig for sketching because it has that option, personally I use inkscape then export to synfig ( that option is provided) You could also go through the videos posted View my first animation - #2 by ktim for more insight this topic