I used to be really awful at Blitz, too. The time pressure got to me and I'd make blunder after blunder, and miss obvious checkmates. When I learned to take some time to gather myself, and not worry to much about the time, I got better.
As for your opening dilemma, really the only thing you can do is study openings. You never know what your opponent might pull off, so try to learn as many as you can.
What is the best way to get better at blitz chess?
I usually play 5 min blitz 5 second increments, and I usually lose to very low ratings. I make too many blunders, and sometimes sometimes I am unsure of what to do in openings(during correspondence chess, I usually use database if I'm unsure)
Thanks in advance