I stay in supercruise and sort the first coordinate first. See if it's increasing or decreasing. Turn to the left and see if it increases/decreases fast or slower.. By turning in different directions you can find the direction that keeps it more or less constant. Once you have that, you turn one way to decrease it and the other to increase it, so that you can guide it to the correct value.
When you have the first co-ordinate at the correct value and you have the direction to keep it there, you can look at the second coordinate. If you stay on the line for your first coordinate, you will eventually come to the exact position you need, but it might take a long time. Remember that the number goes up to 180 and then starts going down again, so -179 is very close to +179.
If you figure that the number is going in the wrong direction for the second co-ordinate, you can do a 180 deg turn by pitching up and then rolling when the planet comes back into view, which will keep you on the line where the first coordinate doesn't change, but left and right to control the number up and down will be reversed..
When you get close, dive straight down to drop out of SC and continue to use the above techniques to home in on the target.
With a bit of practice, you'll soon figure out which way to turn to get more directly to the coordinates.
Once you drop out of SC a compass appears at the top of your HUD, so you can get exact direction to keep the first coordinate constant.