When engaging a Pokemon in battle, throwing the ball at the inner circle when it’s at its smallest is the best way to go. The colour of the inner circle indicates how hard a Pokemon is to capture. Green is the easiest, orange is harder, and red is the hardest to catch. Razz Berries can be fed to the Pokemon to lower the difficulty for the next catch. If the Pokemon breaks free, you’ll have to feed it another Razz Berry to lower it again.
Once a Poke Ball has been thrown, it cannot be picked up again. If a Poke Ball throw hits the inside of the color circle an experience bonus is granted, depending on the size of the circle. You receive 100 XP for Excellent throws (Small), 50 XP for Great (Half), and 10 XP for Nice (Full). You can also spin a Poke Ball around in circles quickly and toss it, which activates a curveball bonus if the throw lands.
Take the time to throw the ball properly; a Pokemon engaged in battle will not run away based on time. What triggers the run-away is the act of breaking out of a Poke Ball. Bringing up the item bag cannot interrupt runaways.
Originally Posted by: gamespot.com