Everybody seems to think that interrupting people is rude. Maybe this is something learned when we are children, with our parents telling us, “Don’t interrupt when I’m talking.”
Interrupting when it is unnecessary is rude but sometimes you simply must interrupt. Here are the ways to do it.
Try to get someone’s attention visually.
Sometimes a raised finger or raised eyebrows is enough. At other times you may need to raise your hand above head height.
This should be obvious but not everyone is polite when interrupting and native speakers are usually the worst. A simple “Excuse me, but I’d like to say/ask something, please.” should be fine. If there is a pause, say what you want to say. Try not to ask if it is all right to ask a question. “Sorry, can I ask a question, please?” is something native speakers do say but it is so weak that someone may simply say no.
Remember, you want to interrupt the conversation, not hijack it. If you interrupt and then give a long speech, people will avoid letting you interrupt in future. Keep it simple: three sentences at the longest.