Are you making a web comic or something?
Your image is a bit too small and the lines are too thick so that they make it so that I can barely see anything.
However in general, you want your text to be shaped like a diamond, visible, lines from the bubble pointing at who said it or at least be near the character saying that dialogue (if the panel is in a first person PoV, then the line should be inverted going into the bubble instead).
Make sure bubbles don't cover up everything that's going on, and for the love of god, don't stuff entire paragraphs into a single bubble, people don't speak in essays.
And be sure that bubbles for thoughts, radio chatter, and other stuff like that have their own borders and font to distinguish them from spoken dialogue.
Also don't be afraid to mess around with the text to make it more fitting, such as in pic related.
t.Typesetter that wanders around these parts