The right size and shape if glass is vital, and makes a huge difference to one's ability to nose effectively. Traditionally whisky tumblers are hopeless. They were designed for drinking whisky and soda - for which they are fine. What is required is a 'snifter' which allows you to swirl the spirit and gather the aromas around the rim. A sherry copita or a small brandy balloon are ideal. The trade use a 'spirits nosing glass', made of crystal, for sharpness and clarity, often calibrated in fluid ounces so you can tell at what strength you are nosing it - eg, if the sample is at 60% ABV and you pour one ounce, then dilute up to the two ounce mark, the drink is now at 40% ABV. 'Black' glasses (they are really dark blue) of a similar style are useful for blind tastings, where you want to hide the colour of the spirit.
Whisky at proof strength anaesthetises the nose and sears the tongue, rendering you incapable of evaluating the sample. Almost all whiskies benefit from the addition of water which, with most whiskies, 'opens up' the spirit by breaking down the ester chains and freeing the volatile aromatics. Very occasionally, one encounters a whisky whose virtues are better displayed neat. Outside the tasting room, many people prefer to drink their after-dinner malts straight - with sound medical justification. In these cases your own saliva acts as the dilutant, and they should be sipped in very small amounts. Blenders nose at 20% ABV, but this can drown some whiskies which tend to 'break up' with too much water. It is always best to add water a little at a time until any nose prickle has disappeared and the sample has fully opened up.