When you get to word balloon placement, here's my pet peeve:

English-speakers read from left to right and from top to bottom. If you want your word balloons to be easy to read, remember this. You can have as many word balloons as you want, so long as you remember that the logical flow goes like this:

A - B -
C - D -
etc.

A very common mistake is to go:

_____A -
B

or, worse yet:

_____B -
A

The reader doesn't know whether to start with the top right balloon or the lower left balloon.

Japanese comics tend to use fewer word balloons per panel than American ones, and this is wise.

Yours for more good comics!

Will