“You ought to go ahead and book it soon.”

Your younger sister is coming to visit you. She hasn't bought her plane tickets yet, and she's waiting to get the best price. You think it's cheaper to buy your tickets early, so you advise her:

You ought to go ahead and book it soon.

(someone) ought to (do something)

There are lots of different ways of giving advice. "You ought to ___" is one form of advice that's used in casual conversation, when the advice isn't that serious or important. For example, you can use "ought to" when suggesting which dry cleaner to use:

You ought to try Lucy's on 9th Avenue. They do a really good job.

go ahead and (do something)

People use this phrase in casual conversation to express doing something soon, instead of waiting:

You guys go ahead and eat — I'm not hungry.

Let's go ahead and pick a day and time for our next meeting.

book (a flight)

To "book a flight" means to buy or reserve your tickets to ride on an airplane. Notice that you use "buy" with "tickets", buy "book" with "flight":

Have you bought your tickets yet?

Have you booked your flight yet?

Other things that you can "book" include:

• book a room (in a hotel)
• book a hotel
• book a car
• book a table (in a restaurant)