I've posted already about how, in my opinion, one of the factors that sets a professional comic aside from a amateur one is the lettering. The problem always boils down to distracting lettering, things that well... just don't look quiet right - rather like how Neo in Matrix Revolutions doesn't look quiet right when he turns into a CGI figure - something just seems ...off.
The easiest thing to fix is the I-problem.
All computer lettering fonts will have two styles of I - there'll be an I with serifs (fancy little nobbly bits dangling off the end) and an I without. (if you're looking fonts, try blambot - fonts are either free or around $20 - about a tenner).
When lettering the serif-I should be used when you're talking about yourself (or when your character is) and the san-serif (san meaning without) should be used within words, for example:
(if you can't read all of it, just click it)
Now, how do you swap those fancy Is? simple, upper-case I is the serif one (for I, Cladius) and the lower-case I is the san-serif one (for I, Claudius).