当想要表达“好久不见”时，可以使用以下几种常用的英语表达：
It's been a long time.
It's been so long.
I haven't seen you for a long time.
I haven't seen you for ages.
Long time no see.
这些表达方式可以根据不同的场合和对话的正式程度进行选择。例如，在较为正式的环境中，可以使用“It's been a long time.”或“It's been so long.”，而在较为随意的场合，则“Long time no see.”会更加常见。此外，还可以结合询问对方近况的话语，如“How have you been？”或“What have you been up to？”来使对话更加自然和友好。