Invoke the Powers

 who will aid you in your work.

One approach is to enlist the aid of a Goddess or God who is likely to be  interested in the specific work at hand: Aphrodite for a love-spell, for example, or Brigid for healing.

Or call a Deity with whom you have a personal relationship.

Or call one of the Deities whose business is to aid workers of magic: Hecate in her aspect of Queen of Sorcery, Hermes who is opener of the way and patron of magicians, or Isis who won the arts of magic from Ra.

If you call more than one Deity for a particular spell, give some though to how and if they will work together. 

When you speak invocations and intentions in magic, it is important to speak them aloud, even when working alone. The difference between disembodied mental language and concrete, audible words can be the first step in bringing your intention through to manifestation.

The best approach is simple and direct. Tell the Goddess or God what aid you need, and why. Welcome the Deity with things known to give pleasure to that Power. A little research on mythology will go a long way; seek out traditional stories and images of the Deity in question for ideas about what they like.