After you determine from first that the ball will land safely in the outfield or make it past the infield on the ground, you need to analyze your chance of making it to third base on the play. Start to flair out on your way to second to prepare yourself for the turn towards third.
If the ball is hit from center to left field, you will have the play in front of you and it will be up to you to determine if you are going to attempt to make it to third or not. Remember, by making it to second, you are in scoring position. Do not take chances going to third if an average to good throw will get you out.
If you determine that you are going to try and make it, make sure you focus on hitting the inside part of the bag as you turn the corner. Once you have made it past second look up and pick up your third base coach. If you look over your shoulder trying to pick up the ball, you'll only slow yourself down. The third base coach will let you know whether to slide or go in standing.
If the ball is hit from right center to right then you must rely on the third base coach to let you know whether to stay at second or go for third. This often happens after you have rounded second base! When you're about 3/4 of the way toward second, you should have already picked up the ball and the position of the outfielder and determined whether you will try for third on the play. Since you only get one chance to take a look, you will want to pick up the third base coach. He may be giving you a sign to stay on second, or to keep running, or he may not know at that point. If you get no sign before getting to second, you must use your determination from the picking up the ball. If it looks like it was hit hard and directly to the right fielder, you will want to go straight in to second base and pick up the right fielder or third base coach as you do so. If the ball was hit down the line or in the gap and you are anticipating trying for third, take an aggressive turn. You must pick up the third base coach immediately after touching second. He will be able to let you know whether to continue on or to stay at the bag. The big difference between scenarios is in the first, you plan on staying at second unless the coach lets you know otherwise; in the second scenario, you plan on going to third unless the coach signals you to stop.
It's essential that you remember to pick up your third base coach once before touching second base and once immediately after touching second base.