Are there any swimming technique exercises I can do outside the swimming pool?

Yes Youtube it

One thing I do is to try to improve my body position.  Your back should be straight when swimming, with your gut sucked in.  You should not be swimming with a sway back, or letting your tummy drag you downwards. This is often initiated by lifting your head out of the water instead of turning it to breathe. Stand up straight with your back against a wall.  Make sure the entire length of your back is actually touching the wall.   Heels against the wall too.  Squeeze your butt-cheeks and tuck your butt down -- suck in your gut -- press your belly button backwards hard so you are firmly touching the wall all down your back. Now lift each leg straight up without bending your knee, about waist high or as high as you can.  Keep your back touching the wall.  Lower your leg and lift the other.  This should be slow and controlled. I can't find a video for that exact sequence, but you can do the same thing while sitting against a wall.  Keep that back straight!  And remember that feeling next time you are in the pool.  You can also do this in the pool, leaning back against the side of the pool with your arms supported on the gutter.

While standing in a room or outside, bend at the waist and pretend you're swimming. Relax and concentrate on syncing your breathing.