A very simple trick to get pastel colors. I've only experimented with this with photos so i don't know how effective it is with anything else.
1.take an image and desaturate
2. Ctrl-b for color balance
3. adjust shadows with a base color ( i usually use yellow for sepia toned images). Not too much though, just enough to get a slight color.
4. adjust midtones in a similar manner
5. ever so slightly change the lightest section as well.
6. This step can be done in the very beginning or last, purely optional to use.
example:
Simple pastels 
Linear Mode
