I lived in England for two year, however, all of these countries are big, you wouldn't be able to see the whole thing in just one vacation.
So first pick out the cities that you think you would like to go to. Do you want to stay in a hotel or hostel? What's your budget?
What time of year? What's the weather going to be like? When it the cheapest time to go if you don't care when you go, do you know anyone in these countries? Pay them a visit if so.
Most people that see the UK go to London. Can't blame them, there is lots to do and see, but just know that the rest of the UK isn't gonna be like that. Would be like saying that all Americans are like New Yorker's.
What kind of food do you guys like? Maybe google what's popular in each city that you would like to see.
Do you want to do touristy things or not?
Now, you don't have to answer all of my questions but that's the kind of things that I think about when I'm planning a trip. And keep in mind that planning the trip is a lot of fun. You get to imagine yourself some where fun, where you don't have to worry about work or school and you get to eat a lot of good food. Get excited about what you guys could see that's new to you.

@Apollo Im Burning: you don’t need to answer all of those questions in here. It will just help you plan.

I live in England and visit France all the time, and I went to Italy on holiday last Summer!

I went to Rome and it was honestly so gorgeous. <3
We tried not to spend too much money, so my friends and I did a lot of sightseeing! There's so much you can see without spending anything or too much, so many pretty buildings. The Trevi Fountain is so gorgeous in the evenings. Venice is apparently really lovely too!

For France - Paris! The Eiffel Tower is honestly so lovely to visit, I've been up it a few times and it was worth it every time. There are some really amazing museums too, and markets to visit and such~

I'd recommend looking up lists of free things to do in wherever you'd like to go, and choosing an basic destination and day-to-day plan based on that! Try and find a few things you'd really love to do and try and link them up for a travel plan!

I hope you have an amazing holiday! :D

@Apollo Im Burning: :D Have a great time!!
You'll have to update the forums here with lots of amazing holiday pictures!