Being a runner on second or third is easier, in some ways, than being on first. It's not that there aren't perils to avoid at second or thirdbase, but the advantages flow to the runner at these bases because most pitchers are better at holding runners at first. It makes sense—pitchers hold runners at first more often than elsewhere. But it's curious how most pitchers—even those with good moves to first—are so poor at holding runners in scoring position. Runners picked off at second and third are almost always caught not by the pitcher, but by the catcher and infielders—true at all levels of play.
Generally, you can get your biggest lead from second. The second baseman and shortstop are at greater distances to the bag; they have to field their positions and thus can't really hold you on. They expend energy faking you back, pounding their gloves or jumping toward the base then sprinting back to position. You can see the second baseman's moves peripherally, and a good thirdbase coach will alert you to what the shortstop is doing behind your back. So you can get three good strides out, and more on your secondary lead. Of course, the higher the competitive level, the greater the likelihood that a catcher can whip the ball to second in a heartbeat if he catches you napping. Middle infielders put on plays to that effect—on a pitch-out, they abandon their position early to beat you to the bag. If the throw's there, you're picked. But at lower levels, you've got more margin for error—the catchers don't make that snap throw.
From third, a baserunner gets a modest lead and watches carefully for the pitcher to go home. The best secondary lead from third involves walking towards home, not running. Running brings you too far—it's only a ninety-foot throw for the catcher to pick you off, after all. But walking toward home puts you in motion and gets you far enough out to break home or break back. You always take this lead in foul ground in case you're hit with a batted ball, and you always return to third in fair ground to block that throw. Better to take a peg in the back than a third baseman's tag in your face.