Theres a lot of good advices already
I highly echo the same advice:
1. CV - keep it updated - fill it out right after each block, I also recommend making a summary of any presentations / projects you're going to list so that you can review it prior to the interviews since they may ask about it. Doing it during the rotations will keep things fresh and saves you the work when its application time.
2. Intervention list - Also what the other poster said, keep a list of interventions, especially memorable ones - write out what happened, what was your role, what you learned from it. Did you have a conflict with a resident or attending? how did you resolve it. I had a lot of situational questions that I answered using experiences during APPE so if you keep a list of it, it'll be easier to draw back to these situations to answer the questions. I used this for situational questions to keep in mind when interviewing:
http://wilkes.edu/Include/academics/pharmacy/PharmInterviewQuestions2009.pdf
3. Have a good idea of who you want to ask for LORs, if you want to pursue a pgy2 in a specialty, it'll be good to get a LOR from that preceptor. Basically, know who you want to ask, make sure they're the type of person that will meet deadlines for you, and do amazing on these APPEs. It'll also be good to know who these preceptors know b/c that will come up if you apply to their alma mater or they did residency there... it IS a lot of who you know.
4. Regional showcases - a lot of regions will do a residency showcase before the ASHP one, def go to it if your program is there, its smaller, easier to talk to people and get to know the programs. They WILL likely remember you when you see them again at ASHP, making 2 impressions! A lot of my classmates went to the regional one and only stopped by briefly at ASHP... you don't have that much time at ASHP (b/c theres SO many programs available to see) so no need to spend a lot of time at the same program if you got all your questions answered at the regional showcase. Because the regional showcases are earlier than the ASHP midyear, its also good to start researching the programs you're interested in early and have your CV ready to go by the regional showcase.
Lastly when its closer to the application period it will be stressful! Ask questions on SDN! I found it to be very helpful to reach out to SDNers. Having gone through the process already, its not terrible, if you do a lot of these things mentioned above throughout your rotations, you will have less work to do once the application period comes.
@Farcus - I heard the same thing, a new system that everyone will complete for all programs... just makes me wonder if there will be more supplemental applications similar to applying to pharmacy school...