dive in with both feet
To begin or undertake something quickly, enthusiastically, and without trepidation. I know you're nervous about starting school, but you just need to dive in with both feet and do your best!
dive in with both feet
and jump in with both feetFig. to become completely involved with something quickly, especially something new. I had never done anything like this before, but I just jumped in with both feet and learned it in no time.