Thank you Brenna, I will keep all of your amazing information in mind when on the horse.
Yes Tim, it is a gp saddle. I'm used to riding western, just don't feel like packing my heavy saddle, and want to try something different.
Some people find that English saddles push them forward. Be sure to lean back and sit up straight.
Also make sure your stirrups aren't too short. This can throw you off balance and mess with your centre of gravity.
If you'll be posing, make sure you aren't just letting yourself fall heavily back into the saddle, but that you are slowly lowering yourself into it.
Assuming you rode western before, many people who haven't ridden English before find the saddles very insecure and find it difficult to balance in them. Don't be aftaid to grab the mane/martingale if you feel at all unbalanced.