a good brush is vital ( by good i mean a good point not a small brush) i use a gw basecoat brush 90% of the time, because of the great point it holds and the well of the brush holds well.
next good consistency, thin, very.
then the correct ammount on your brush, too little and the paint will dry before and during your execution of your stroke, too much and you will not have controll of the paint.
last hold the brush close to the tip and be confident and precise. go fer it!