1.Spray some cutting fluid, WD40 or other oil to aid in cutting.
2.Hold the tap in line with the t-nut and turn it clockwise. Try to keep it very straight as you turn, this is important.
3.Every few turns, back the tap out (counterclockwise) to clear away chips of loose material.
4.When the tap has passed through the t-nut, back it out, clean out chips and any cutting fluid or lubricant, and try bolt using your hand at first.