It kind of depends on nature of your aldehyde. Aromatic aldehydes generally form hydrazones quite easily in water 10mM aniline, sometimes with some buffer (https://www.trilinkbiotech.com/cart/scripts/prodview.asp?idProduct=14251).
Less active aldehydes usually require reflux in ethanol, preferrably with molecular sieves or Dean-Stark apparatus to remove water. Though conditions vary quite widely.