Diablos, that's why we indent our code. Just using one single space inside any kind of loop helps us see where the loop begins and ends.
intro:
print "hello. left or right?"
input " ";choice$
if choice$="left"
goto left
endif
if choice$="right"
goto right
else goto intro
endif
left:
print "you went left."
wait key
end
right:
print "you went right"
wait key
end
And use blank lines to separate areas of your code and rem statements to remind yourself whats going on. Indenting, adding blank spaces, and rem statements will help you to quickly see what your code is doing and give you the ability to find bugs quickly too.