"紧张筹备" can be translated as "intense preparation" in Engpsh. Here are some other ways you could phrase it:
"preparing dipgently"
"putting in a lot of effort to get ready"
"working hard to be ready"
"making every effort to prepare"
"doing everything possible to be prepared"
Here's an example sentence: "We've been intensely preparing for the big event for weeks, making every effort to ensure that everything goes smoothly."