First of all colour some pages in preparation. I've used some spent procion dye for this but any water based medium will work. Then you need to select a strong image from your previous pages that can be reduced to an outine shape. Draw this into some card. Cereal packet weight will be fine. If you want to do a lot of stencilling then it's worth cutting your stencils from acetate sheets but I find card works well enough for a few applications.
Carefully cut around your outline. It's worth doing this carefully because then you can use the cut out shape too.
Position your stencil onto the page. I use a little bit of spray mount to hold it in position because I never seem to be able to stop the stencil slipping if I try to hold it in place, although I'm sure some masking tape would work too.
For the first exercise I've used Markal paintsticks (Shiva sticks) which are pure pigment held in an oil and wax mixture. If you are not familiar with them I can recommend this book by Ruth Issett which is available from ArtVanGo (along with the paintsticks)
Apply the paintick around the edge of your stencil. Apply generously and use more than one colour.
Now using a toothbrush (I recommend you use one just for this and not your husband's), brush the colour from around the edge of your stencil into the space on your page.
When you feel you have transferred enough colour, lift your stencil and your should be left with a clear strong image. You could of course do this onto a white page and then apply your water based paint. The paintstick will provide a wax resist as in the last sketchbook post.
You can then repeat the process on different parts of the page. If you use the same stencil without applying additional paint stick you get fainter, shadowy images. (I'm already thinking sheer fabrics here!)
If you don't have paint sticks you can still use the stencils with acrylic paints or some other thicker paint medium. Put your stencil back on the page as before.
Load up a brush (preferably a stencil brush which has a flat end) with paint and then remove any excess paint on a scrap of paper. Your brush should be quite dry.
And with quick jabbing movements apply the paint through your stencil.
Use more than one colour to create dappled shadowy effects.
When you've applied enough paint, lift your stencil and your image should be transferred to your sketchbook.
At this stage don't forget the piece of card you cut from your stencil, as this can be used as a mask. Stick it down on your page with masking tape or spray mount.