New to open water

As Gdavis said, it is very helpful to do non-stop swims for the duration you think it will take you.  When training for 10Ks, I would do 2 hours non-stop swims.  I would also do sets like 80 x 100 with 10 secs rest, 40 x 200 with 20 secs, even 20 x 400 with 20 seconds rest.  All of these help your body get used to the non-stop activity.  Do one of these non-stop swims 1x/week until your swim.  Don't know how old you are, when I was 40 and doing this, I would target 150 heart rate.

During your pool swims, start practicing lifting your head during a breath to look forward for sighting.  You don't want to do this alot as it is very tiring, but once every 20-30 strokes in an open water race is a good frequency.  Are you required to have a kayak or canoe escort?  if so, that changes some of the dynamic in this regard.

Aside from training, it is helpful to be very comfortable breathing to either side - even if you are predominantly only one sided.  This is because, at some point, the waves are likely to keep you from taking a breath and being able to switch to the other side will help.  In a couple of races, the waves actually rolled me over.  if this race is in Lake Michigan and the swim is along the shore and out and back, you do not want to breath into the waves the entire race.

Also, invariably, you are going to choke on water and want to dry heave.  It is an awful feeling, but can be done while you keep swimming.  Hard to practice this - just be aware it will happen.

Depending on the number of people, the start and during the race could include a fair amount of incidental contact with other swimmers.  This can be unnerving, so find a way to get used to tight quarters.  When I coached open water, I would have 8-10 swimmers try to fit side-by-side across a 2 lane distance and swim together just to get used to the feeling.

Good Luck!

As Gdavis said, it is very helpful to do non-stop swims for the duration you think it will take you.  When training for 10Ks, I would do 2 hours non-stop swims.  I would also do sets like 80 x 100 with 10 secs rest, 40 x 200 with 20 secs, even 20 x 400 with 20 seconds rest.  All of these help your body get used to the non-stop activity.  Do one of these non-stop swims 1x/week until your swim.  Don't know how old you are, when I was 40 and doing this, I would target 150 heart rate.

During your pool swims, start practicing lifting your head during a breath to look forward for sighting.  You don't want to do this alot as it is very tiring, but once every 20-30 strokes in an open water race is a good frequency.  Are you required to have a kayak or canoe escort?  if so, that changes some of the dynamic in this regard.

Aside from training, it is helpful to be very comfortable breathing to either side - even if you are predominantly only one sided.  This is because, at some point, the waves are likely to keep you from taking a breath and being able to switch to the other side will help.  In a couple of races, the waves actually rolled me over.  if this race is in Lake Michigan and the swim is along the shore and out and back, you do not want to breath into the waves the entire race.

Also, invariably, you are going to choke on water and want to dry heave.  It is an awful feeling, but can be done while you keep swimming.  Hard to practice this - just be aware it will happen.

Depending on the number of people, the start and during the race could include a fair amount of incidental contact with other swimmers.  This can be unnerving, so find a way to get used to tight quarters.  When I coached open water, I would have 8-10 swimmers try to fit side-by-side across a 2 lane distance and swim together just to get used to the feeling.

Good Luck!

Thank you for the response!! I'll work on incorporating longer and longer nonstop swims. I actually am a bit nervous for the volume of people, I've swum in very crowded conditions before but never in a race setting so I'm going to try and find some local groups to practice with if I can. 

Definitely comfortable breathing on both sides so I'll try to get used to picking my head up as well. There should be canoes/kayaks at the race.