Generally I use a Synchronise Pokemon (such as Gardevoir or Alakazam), with a damaging move, recovery, status (either sleep or paralysis), and then another (much weaker) move to lower the original Pokemon's health and start an SOS chain. What Synchronise does is it makes a 50% chance for wild Pokemon to have the same nature. In this case, there is a 50% chance for wild Pokemon to have a Bold Nature (+Def, -Atk). My capture Alakazam is as follows.
Alakazam (M) @ Leftovers
Ability: Synchronize
EVs: 252 HP / 252 Def
Bold Nature
IVs: 0 Atk
- Thunder Wave
- Recover
- Psychic
- Signal Beam
So Thunder Wave is really useful for catching Pokemon, as it spreads paralysis, and can stop the target moving, thus saving their PP so you have more turns to catch it. Recover is an absolute must, as it enables 'Kazam to regain health, and also stall turns. Psychic is a standard STAB attack, used for weakening stronger foes, and also for killing Pokemon called in via SOS. Signal Beam is a much weaker option, so is used to lower health. It also covers Dark types immune to Psychic. However, the chance to make the target confused is irritating, as more than once I have seen a shiny die due to hitting themselves in confusion.