Your chosen site should be in good light, as snowdrops will not grow well in dense shade. The dappled shade from deciduous trees or shrubs is ideal, although the elwesii forms will tolerate more sun quite happily.
The soil can range from alkaline through to low acidic and must be fertile and well drained. Snowdrops will not tolerate excessively wet soil, a problem for some with the recent wet winters we have experienced, so to ensure adequate drainage grit/sand or perlite can be incorporated into the soil.
To increase the fertility of the soil humus in the form of leaf mould or well rotted garden compost can be incorporated into the soil prior to planting. Do not use composted bark; in my experience, this can cause botrytis.
A mulch of either organic material (leaf mould, compost, bark chips) or inorganic (sand, gravel) can be applied in autumn. This helps to conserve moisture and helps to avoid soil splashes on the flowers.
Planting bulbs can either be in spring (in the green) or in late summer (dormant bulbs)