make hay while the sun shines 未雨绸缪;把握时机;抓住时机;抓紧时机行事

【例句】
If you want to become a millionaire, you must make hay while the sun shines.
如果你想成为百万富翁就必须把握时机。

If you want to be successful before thirty, you have to make hay while the sun shines.
如果你想在三十岁前成功，就要抓住机会，以免错过良机。