Getting a full bridge

Hi Veeners :) I started some of the flexibility lessons yesterday (so helpful - thanks Veena!) and found that I can't lift into a bridge. I can do a half bridge, but when I try for a full bridge I push and push with my arms but can't lift myself at all, not even a few millimetres. I guess this is a strength issue in my arms, and wondered if anyone had tips on exactly which muscles I should work on strengthening before trying again. Thanks for any advice!