A travel planner who has been on over 25 cruises has shared her biggest no-no's when it comes to cruising - and if you don't heed her #1 tip, it could cost you thousands of dollars. 

Cruising is a travel method that many enjoy for its convenience and ease. Once you book your cruise holiday, you're all squared away - all you have to do is show up.

However, like any method of travel, there are things you definitely should keep in mind before you get ready for your trip. For example, on planes, flight attendants have revealed the one thing that passengers should never do on a plane.

Similarly, there are big no-no's that travel experts stress are important to keep in mind. In fact, travel expert Jennifer Greene, who works for cruise-specializing agency MEI-Travel, recently revealed a list of helpful things to keep in mind before you set sail for your vacation.

Jennifer says one of the biggest mistakes that could cost you big time is flying to your cruise starting port the same day the cruise departs.

Say, for example, you're flying out of Miami. The worst thing you can do, Jennifer says, is to fly into Miami the day your cruise departs. Why?

"There's so much uncertainty with air travel, and one minor issue could cause you to miss the boat. You also need to factor in getting your luggage and traveling to the cruise terminal from the airport - some terminals are 15 minutes away and others are over an hour," she notes.

If you end up missing your departure time, you could literally lose thousands of dollars, all because of an airline malfunction. Don't let that be you!

While this mistake could be the most costly, there are a few other tips Jennifer shared too.

Don't book your cruise for the wrong season
"Timing is everything when it comes to cruising - when you go is just as important as where you go," Jennifer says. If you're hoping to do a cruise to Bermuda, for example, book it for the months when you're sure the weather will be good - there's nothing worse than having a frigid tropical vacation.

Make sure you check whether your cruise is all-inclusive or not
When booking cruises, cruise lines sometimes add fees to your final bill. When examining your payment, make sure you get confirmation on whether the cruise is all-inclusive or not, because it would really be a bummer to show up and think that all of your meals and drinks are paid for when, in fact, they're not.

Don't overpack
Anyone who's been on a cruise knows two things to be true. One, the staff usually loves to make towels into little animals and hang them all over your room (we love this bit.) Second, the rooms on cruise ships are typically pretty small, so it's best not to overpack for your vacation. You don't want to be tripping over all of your belongings on the floor whenever you're in your room.

So, yes, that means you may have to leave some of your best swimsuits behind - maybe you can bring just a couple, instead of 10!

Book your add-ons in advance
"If you absolutely want to secure a certain shore excursion, find out how far in advance your cruise allows you to book the experience and try to make the reservation that day," Jennifer says.

Similarly, cruises also might offer discounted packages on Wi-Fi, food, excursions, and more if you book them ahead of time, so make sure to sort that out before you leave.