If you are finishing over another finish like lacquers, varnish or another water-based system, sand the surface with 400 grit sandpaper then wipe with denatured alcohol. This will give a good micro-scratch for the new finish to bond onto. If you use shellac, sand with 320 after it is dry and remove all residues with a clean towel and a bit of water. Once you have base coats of the Oxford down, you can apply your topcoats. Never use steel wool if you plan to continue the finishing process with more waterborne coatings-rust spots can appear if you have not removed all of the microscopic steel dust from the finish.
Pads are ideal.
They are available in various sizes and the smallest can be used for intricate work. When you brush, pre-condition the brush by first wetting it for a moment in water, then wring out the excess. Dip only halfway up the bristle length and then apply the finish to the surface. Unlike solvent-based varnishes, you do not have great deal of open time before it starts to dry and setup, so try to work quickly. The worst thing you can do with a water-based finish when brushing is to fuss with it.