Tap the rolled sponge into the lightest colour ink first, dab onto a piece of scrap paper first to remove excess ink, then tap gently round the edges of the circle, slightly firmer near the edges - I never go right into the centre of the circle with ink as this gives a more graduated finish (example). Follow the same process with the darker ink until you are happy with the shading.
Lift the mask off, allow to dry for 5/10 minutes, or give a blast with your heat gun, then you are ready to stamp your images.
The next technique takes it a step further as you create a mask for your sun/moon and image. This is useful if you want to use very light colours for colouring your image as there is no underlying colour to conceal.
Stamp (and emboss if you wish) your image onto a piece of good quality cardstock. Stamp it a second time onto a post it note, piece of paper or if you are really posh masking paper !
Cut our the second image and lay it over the main image, then lay your mask (sheet of paper with the circle cut out) over the image where you want to see the sun/moon. Follow exactly the same process as the first technique above. Lift of both the circle mask and the main image one and you are left with the sun/moon behind your image.
Basic brayering technique. There is no limit to how far you can take brayering and some wonderful effects can be created, but here I will stick to the sun/moon again with a few hills thrown in for good measure. Basic materials: Ink pad, big and juicy are by far the best as apart from the blend of colours, they are large enough to accommodate the brayer - I always use a speedball brayer as they are soft and give a nice even finish. A circle - paper rather than card is best as it is less likely to give off shadows as you roll the brayer across. Non permanent glue. Gloss cardstock - in my view essential as a matt cardstock can absorb the ink, is harder to work with and is less likely to give an even finish.
Once you have removed the excess you need to do a wheelie - assuming you are starting to brayer the top half of your piece first (and right handed) you will need to do the wheelie on the left hand side of the brayer. This removed the ink from the edge and will prevent lines in the middle of your cardstock.
Gradually build the colours up with light movements drawing the brayer towards you. When you are happy with the colour, turn your cardstock round so the bottom becomes the top temporarily (there will be no ink on that part yet) then continue with the same process and you will end up with graduated colours over your whole piece.
Next tear a piece of plain paper, lay it over your brayered piece, ink up your brayer again and remove the excess and brayer more ink across the top of your piece of cardstock (part of your brayer will be inking the piece of paper). Move the paper down and repeat and you will see your hills building.
This picture is pretty poor as I did the photos under my daylight lamp, but the hills are just visible. These are clearer.
Remove the mask from the sun/moon. Scrunch up a piece of plain paper, ink up your brayer, take off the excess ink, do a wheelie on the left side again then roll with a fairly hard movement over the piece of scrunched up paper. Run the brayer over the top half of the card and you will create a clouded effect over the sun/moon - just about visible in the picture. The same technique gives great water effects if you want to create water/sea (see here).
I really do hope this makes sense, not the easiest thing to explain on paper, so as always any questions just yell.