To write effective dialogue, start by listening to real conversations. Notice how people interrupt, talk over each other, and use body language (which you can translate into dialogue tags or descriptions). For example, if someone is nervous while talking, they might stutter or use filler words like 'um' or 'uh'.
Use subtext in your dialogue. Characters don't always say exactly what they mean. For example, a character might say 'I'm fine' when they're clearly not. This adds depth to the conversation and makes the reader dig deeper to understand the true meaning behind the words. Also, be aware of the cultural and social context of your characters. Their dialogue should reflect their background and the world they live in.