How can fear be used to aid one's spiritual development?

Having fear of anything that will destroy your soul. "Without fear there is no hope" So fear is a good thing. As long as it is used properly.

Do you mean:

Proverbs 1:7 The fear of the LORD is the beginning of knowledge, But fools despise wisdom and instruction.

If so, it is defined as:

Proverbs 8:13 The fear of the LORD is to hate evil; Pride and arrogance and the evil way And the perverse mouth I hate.

A fear (respect and concern for judgment) of God has the following benefits:

Psalm 145:19 He will fulfill the desire of those who fear Him; He also will hear their cry and save them.

Psalm 147:11 The LORD takes pleasure in those who fear Him, In those who hope in His mercy.

Proverbs 14:27 The fear of the LORD is a fountain of life, To turn one away from the snares of death.

Proverbs 19:23 The fear of the LORD leads to life, And he who has it will abide in satisfaction; He will not be visited with evil.

Good question.

Isn't fear the basis for evil ?