The technique that always frustrates me is probably an older one - you use 3 different re-inkers and a baby wipe. Drip 2 or 3 spots of each re-inker onto the wipe - the colours should run into each other and make a unique "stamp pad". I learned to do this at a workshop - ordered the re-inkers and the stamps we used - and have NEVER been able to reproduce those results - it always ends up being a blotchy, yucky mess.
For the people having problems with watercolouring - I use watercolour paper, a damp to wet fine paintbrush, and a stamp pad. With the pad closed, squeeze the lid down onto the ink pad. Open the stamp pad up, and you should have a pool of colour on the lid. Dip your paintbrush into the ink and go about "painting" - you can adjust the depth of the colour by how much water you use for your brush. HTH!