tuesdays usually have cheapest fares (dont have to fly on tuesday, but if you buy your ticket on a tuesday you generally get the best price)
like has been said kayak is good for comparing, i also like to use bing.com/travel for comparing plane tickets, their price predictor feature (tells you if they think fares will go up or down and their degree of confidence) makes me feel better about buying tickets when i do. after comparing flights on those sites and finding the one i want ill usually go to whatever airline's site and book directly from there
i cant remember where you said you're flying in the OP but if you're travelling across country in the winter is best to avoid cities that are prone to bad weather. don't want to hit delays trying to make a connection. generally take connections in southern cities over northern ones
reward miles are great, signing up for credit cards for the bonus is a good way to get "free" flights (signed up for 3 different cards for this in the past few months haha). unfortunately that probably wont help you with your flight coming so soon. it can take a while for the miles t o post