1. TEXT :
Try to avoid using only 1 word for each line, it's hard to read
DON'T
DO
IT
LIKE
THIS
Try to add short words into 1 line
DO IT
LIKE THIS
INSTEAD
2. COLORS :
If you are aiming for webcomic audiences, you should try to add colors, if you don't have time, try to use at least one color, like this
It's easier to get people attentions, screentones is actually means for printing purpose, don't need to force yourself to use them, look like they took you a lot of time.
3. PLOTS :
First impression is important, try to make something interesting to see in the first chapter and make people look forward the the next chapter, explaining the world, 2 guys staring at each other is a little too boring I think.