Some suggested lettering conventions.

In general, we follow Blambot's Comic Book Grammar & Tradition.

Balloons

Text must stay in the live area.
All readable text needs to be inside the template live area. The balloon can extend out of the live area as long as the text is safe.

Balloons need consistent padding.
Make sure the dialog text isn’t cramped up beside the border. The spacing between the text and border should be consistent on all sides. Spacing should be consistent across the story as well, unless it’s a deliberate choice.

Don’t obscure faces, hands or figures.
If possible, make sure the text doesn’t conflict with key elements of the artwork.

Balloons don’t have to stay in the same panel the script placed them.
Feel free to migrate a balloon to a different panel if the story would read clearer. Sometimes this is necessary for cramped panels.

Minimize ragged edges and danglers.
Captions should be justified or centered. We want text blocks without ragged lines or danglers.

Text

Lettering should be digital where possible.
Hand-lettering can be difficult to update on short notice. SFX can still be hand-lettered if you'd like.

Short numbers are written out.
"Table for two, please."

No lowercase.
All text must be in an uppercase font. "WE ALWAYS SHOUT HERE."

No spaces before or after an ellipsis.
"That’s tough...cookies."

Three dots in an ellipsis.
"Yep…"

Always double-dash for sentence fragments OR in place of em dashes.
Em-dash and single dashes are not used in comics. No spaces on either side of double dashes! "But you promised--!"
"The rear axle began to make a noise--a grinding, teeth-gritting rasp."

Line spacing.
Text should be neither too tightly packed or too distantly spaced. In general, for 8pt text, 8 or 9pt spacing should work.

Punctuation goes inside quotation marks.
E.g; "What do you mean, 'funny-looking?'"

Avoid tangents.
Tangents are distracting and confusing. See the Blambot rules.

Avoid stacking the same word on adjacent lines.
Doesn’t come up often, but best not used unless intentional. It can be distracting.
"This house is scary."
"This house is also smelly."

Consistent font sizes and spacing
All dialog and captions should have the same font size and spacing, unless there is a specific emotion being invoked. I.e: a whisper or a shout.