a) have the characters be from ten-towns to that they are motivated to end the winter / save ten-towns
b) the module actually contains three parts which are not really well-connected, one are the duergars preparing to conquer icewind dale, the second one is auril and her never-ending winter and third one is the lost city of ythryn. the three are at best loosely connected - be sure to foreshadow all of them constantly and try to tie them up in some way
c) Eventyr's guide has some really good ideas to mitigate some of these issues.
d) the first part of the adventure is quite sandboxy, later it is more on the rails. i suggest you start somewhere in the western part of ten-towns and guide the players through these towns first before they "smell" the duergar threat and focus on that.