You shouldn't have to do anything for the Half-Yearly. The Anniversary Sale usually has a few "preview" days for Nordstrom Rewards members, and that can sometimes require a reservation because you're supposed to be accompanied into the tented sale areas by an SA. The only Nordy's shopping event I can recall needing to specifically RSVP to is the Holiday Shopping Party.
Here are the dates for all of the Nordy's sales in 2014 (in-store and online):
• Half-Yearly Sale for Women and Kids—starts Wednesday, May 21
• Half-Yearly Sale for Men—starts Friday, June 13
• Anniversary Sale—starts Friday, July 18 and ends Sunday, August 3
• Half-Yearly Sale for Women and Kids—starts Wednesday, November 5
• Half-Yearly Sale for Men—starts Thursday, December 25 online, and Friday, December 26 in-store