I use oxpho blue quite a bit. A couple of things I learned is -
1) degrease with acetone. I used to degrease with denatured alcohol and found that it seemed to absorb the moisture/humidity and would end up with small rust spots in the finish.
2) Use disposable gloves, you don't want fingerprints on your metal. Plus it is best if you keep it off your skin.
3) Do not work from the container. Pour a small amount(however much you think you'll need) into another container and work from that as to not contaminate the original liquid.
4) I usually apply, let it set on the metal for a minute or so, then rub back with degreased steel wool. No need to get crazy, you just want to level/even the finish. If I need it darker, I repeat.
5) Once finished and satisfied with the color/tone, I apply a coat of wax.