Size:
* Tiny: Extremely small
* Little: Somewhat small
* Miniature: Very small, often referring to scale models
* Compact: Small and neatly arranged
* Diminutive: Very small in size
* Petite: Small and dainty, often used to describe people
* Scanty: Insufficient in size or amount
Quantity:
* Few: A small number
* Limited: Restricted in quantity
* Sparse: Thinly scattered or distributed
* Scant: Not enough; insufficient
Importance:
* Minor: Unimportant
* Trivial: Of little importance
* Negligible: So small as to be insignificant
* Insignificant: Of little or no importance
Other:
* Slight: Not large or important
* Narrow: Limited in width
* Short: Not long in length
* Young: Not old or mature
* Simple: Not complex or elaborate
The best synonym for "small" will depend on the specific context and the message you are trying to convey.