Well you know how a bad workman blames his tools? When using gloss paint it may well be your tools letting you down, a good quality brush is essential, a black china bristle brush is the best tool for the job! Don't load your brush with too much paint as that is sure to lead to drips in your gloss. Using long soft strokes going back and forth over the same area will help to ensure an even thickness preventing those annoying paint drips and runs! Don't be scared to thin the paint a little, although it may seem strange the thicker the paint the more likely it is to run.