You’re skilled in going unnoticed. While using Stealth, you can move at your speed rank minus 1 with no penalty. Faster than that, up to your full speed, you take a –5 circumstance penalty to your Stealth checks.
If you have cover or concealment, make a Stealth check, opposed by an observer’s Perception check, to hide and go unnoticed.
If others are aware of your presence, you can’t use Stealth to remain undetected. You can run around a corner so you are out of sight and then use Stealth, but others know which way you went. You can’t hide at all if you have absolutely no cover or concealment, since that means you are standing out in plain sight. Of course, if someone isn’t looking directly at you (you’re sneaking up from behind, for example), then you have concealment relative to that person.
A successful Deception or Intimidation check can give you the momentary distraction needed to make a Stealth check while people are aware of you. When others turn their attention from you, make a Stealth check if you can reach cover or concealment of some kind. (As a general guideline, any such cover has to be within 1 foot for every rank you have in Stealth.) This check, however, is at a –5 penalty because you have to move quickly.
You can use Stealth to tail someone at your normal speed. This assumes you have some cover or concealment (crowds of people, shadows, fog, etc.). If the subject is worried about being followed, he can make a Perception check (opposed by your Stealth check) every time he changes course (goes around a street corner, exits a building, and so on). If he is unsuspecting, he only gets one Perception check for the scene. If the subject notices you, make a Deception check, opposed by Insight. If you succeed, you manage to pass off your presence as coincidence and can continue tailing. A failed Deception check, or being noticed a second time, means the subject knows something is up and reacts accordingly.
D20Hero SRD Skills article- http://www.d20herosrd.com/4-skills