Most crucial factor is the water stress since the cuttings may easily desiccate until they have formed water-absorbing roots. In general, the humidity must be kept high during root formation, e.g. by keeping the cuttings under a misting system or at least under a cover. Evaporation from softwood cuttings can be restricted by partial leaf pruning.
Cuttings should be rooted under shade. The requirements and tolerances in terms of light and temperature etc. varies according to species.
Cuttings are easiest rooted under tunnel or greenhouse conditions, since several factors can be manipulated and controlled under these conditions.