In the City 3-D stage, the tanks in the left lane will not hit you if
you fly in the right lane at the bottom of the screen. Note, however,
because tanks in the right lane can hit you. Don't rely on this trick
unless you learn the attack pattern and know when tanks will appear in
the right lane.
In the next 3-D stage, the caves, no enemies outside the cave can hit
you if you stay in the lower right corner of the screen. Don't rely on
this trick unless you learn when caves appear on the left side of the
screen. Otherwise, you won't have time to get in front of the cave and
you'll crash.