Asatruar, what is the next Asatru holiday?

and how do you celebrate it?

Winter Nights, which is I believe from 29Th October to 2ND of November.

That depends on your kindred and the Gods, wights and ancestors you worship. Some groups may have a end of harvest festival between 21st Sept and 1st Oct, otherwise Winters Nights is the first big festival of the winter feasting season, it is held any time between 14Th Oct and 31st Oct, for Iceland it is between 14Th & 18Th Oct for more southerly regions it gets later. If you live in a pagan but not 100% Heathen community it can be moved to 31st Oct and everyone can join in with a Miltie-faith "Start of Winter feast".

Winter Nights which I generally hold mid-October. Sometimes I'll hold off until Novemeber honestly. The rule in Texas is that you don't have Winter Nights until you can turn the AC off.