When you put your hand on the Pokéball, a small circle on the target will pokémon. The smaller the circle, the more likely we are to get it. That's right: be sure to pull the Pokéball well. It will take a while to get the necessary expertise, but worth it.
If the circle is green it means it is easy to capture. Yellow is moderate, red is difficult. Remember that best types of Pokéball need to get more powerful pokémon.