First and foremost I find it really helpful to consider how much I am willing to spend and therefore what my bank account should look like when I get home, we (almost) all have bills to pay after all! If this doesn’t coincide with the plans you make in the next steps you will likely have to re-evaluate. Save more and spend more or change your priorities while travelling to fit into a tighter budget.
What kind of trip would you like to take?
Will this be a luxury trip full of spa days at 5-star hotels and dinners in fancy restaurants before drinking the night away in exclusive clubs? Or perhaps you will only bring what you can comfortable carry on your back and your nights will be spent in dorm rooms with as many other people as possible? Maybe something in between?
Of course, nothing has to be black and white like this but I highly recommend you have a general plan. Maybe you want to stay in nice hotels, but to help even out the cost you’re planning to take public transit or walk. There are tons of great ways to keep the overall cost low(er) without having to sacrifice everything.
When should you book?
As far as I’m concerned, giving yourself as much time as possible is always best. Have you ever seen those articles that state plainly that booking on Tuesday between 2-6pm exactly 4 weeks before travel is GUARANTEED to be the best price you will get? I personally think that's a bunch of BS. Of course, depending where you live and depending where you are going makes a big difference too. Travel within Canada is very expensive, but seat sales come up all the time so starting to look as early as possible is best. Plus, if the seat goes on sale before you leave, many airlines will refund the difference! I have also found that when booking and paying for flights far ahead of time the trip doesn't feel like such a big expense all at once. Of course, nothing has to be black and white like this but I highly recommend you have a general plan. Maybe you want to stay in nice hotels, but to help even out the cost you’re planning to take public transit or walk. There are tons of great ways to keep the overall cost low(er) without having to sacrifice everything.
When should you book?
If you aren't tied down to a specific date, I would recommend the WestJet low fare finder as it shows you the best prices for an entire month. As well, try the Hopper app! It will watch all airlines for the best price on the days you select, it will also let you know if the price is going up or down and when the best time to book will be.
When is the best time to go?
Consider what you would like to do. Now consider the most ideal weather to do that. You want to swim in the alpine lakes so maybe November isn't the most ideal time to visit Switzerland. Are you open to whatever adventure is thrown at you and have a flexible work schedule? Go during the cheap season then! Cheap season also means it isn't tourist season so it's a win-win really.
How long is the trip?
Is this going to be a weekend getaway or an open ended exploration? The latter is clearly the one that would take more planning. What should you do about your vehicle/job/home/etc.. If it's long term will you work along the way? Do you need a visa? Will your health and lifestyle allow you to be on the road for a long period of time? There are a great many things to consider when deciding how long to be away for.
The Details
Once you've answered some of these bigger questions you can break it down into the smaller areas.
Will you stay in a hotel, hostel, camp or perhaps try couch surfing? Could you stay with family or friends?
Are you planning to eat in restaurants, have fast food or buy everything from markets and cook for yourself?
Is renting a car realistic or would public transit be better? You could also rent a bike or walk.
Will you be going to museums, galleries or events? Maybe you simply want to see the city and it's architecture.
Is your destination road trip-able? Could you take a train or do you need to fly?
So many things will affect the over-all cost of a trip, but in the end the best thing you can do is get on Google and look up as many real prices as you can. Find out the average cost of a hotel stay at your destination. Try to find out if food is more or less expensive than what you have at home. If you have things that you MUST see or do, find out exactly what they will cost you.
Be specific!
Create a DAILY budget. Have $x available to spend on accommodation, $x on food, $$$ on transportation, entertainment, etc.. Knowing what you plan to spend in one day will then give you the total for the whole trip. And don't forget to include incidentals in the budget! You never know what could happen and having that extra money might just save you! I budgeted $50/day of my trip in the event I had to cover something significant like a new plane ticket or medical expense.
Write it down!
My final tip is to write everything down. Scribble it out on a napkin or type it out on the computer. Whatever you decide to do, having a set budget that is tangible can help to keep you within those guide lines when you really want to spend more than you should.
If you said it would be $35/night at hostels you should do your best to stay within that price range. If you want to splurge on 1 night in a gorgeous hotel, consider taking it out of another area to keep everything balanced.
But don't forget, spend your money on what YOU love! Just because The Eiffel Tower is a "must see" does not mean you must see it.
If you are interested in seeing some real numbers you can read THIS POST. I break down the cost of 5 months in Europe and also share a few other stats.
I hope this has been helpful for you!