Sometimes putting on a new radiator hose can be a monumental task. Stretching and pushing the hose end over a water pump bib or radiator outlet can take all the energy you can muster, not to mention result in skinned knuckles. There's got to be a better way, right?
Yes, there is, so bear in mind that rubber needs two conditions to allow it to flex and stretch: temperature and lubrication. Cold rubber doesn't stretch very well, so keep the hose indoors overnight before you attempt to put it on the fitting. Alternatively you can heat it (carefully!) with a heat gun or just put the end in your pocket for a while.
Lubrication is essential to get a hose to slip over a connection. The best materials to use are silicon lubricant, soapy water or Armor All. Just wet down the inner surface of the hose and push away, being careful not to bend or otherwise damage delicate copper, aluminum or plastic hose fittings.
Don't use petroleum-based grease or oil. It might react with the rubber eventually and cause failure.