preparing A LOT:
i myself don't have much experience with this, but if you want to know exactly when you are going where and doing what for how much then i'll try to put myself in your position and see what would be logical to do...
step one
first of all, decide to which country you want to go to and for how long. do research about visa requirements and the stuff you want to see/do when you're there, using a travel guide (or just go online). i'm a big fan of the lonely planet because it's one of the few travel guides that talks about gay stuff and it is focused on budget travelers. anyway, you can always just choose another guide if you prefer something else. just check how old the guide is, since tourism always changes. you don't want to find out that some tour or museum isn't there anymore when you're already in the country, it's a waist of time and money! reading about other countries is already half the fun and teaches you so much. make sure you always respect the way people are and the way different cultures do things so you won't piss anyone off or make a total ass of yourself (although that does create good anecdotes).
money
so once you've acquired some sort of itinerary it's time to think about money. write down (using your guide and other information you've gathered) on your itinerary how much you'll spend on food, accommodation, transport and the stuff you want to see/do (that includes partying), add it all up and you're done. make sure though, you have some extra cash on the side (or a credit/debit card), just for emergencies and things that will happen outside of you itinerary because trust me, they will. you're gonna need a converter if you're going to a country that uses a different currency. some people don't have any trouble saving money but if you do, it's the best thing to give yourself an amount and a deadline when you want to have saved that amount. then you simply calculate how much you have to save a week/fortnight/month, but make sure it's a reasonable amount compared to your income. if you really want to force yourself, book a flight ahead and you'll have no choice! speaking of flights, if you ask me, trying to find a cheap one is the worst part of traveling. there are some budget airline websites with an overview of different airlines going to different countries, but i still haven't found one that is actually finished, so your best bet it to just check out this list where you will find the links to the airlines themselves. it's a total bitch comparing and searching loads of flights but if it means saving a lot of money than it's totally worth it. make sure you always read the terms and conditions before booking, so you'll won't find any unwanted surprises along the way.
now what?
ok, your flight is booked, itinerary is done and you're saving up. now you have to make sure you book everything that needs to be booked in advance (accommodation, tours, transport, tickets to theater/art/music stuff, special parties etc).
and then all you have to do is just get very excited as your trip approaches!!
preparing SOME:
this is more my style. some things have to be prepared though, otherwise you're screwed. things like having the right visa, a flight in and out and enough money are definitely a must, so make sure that's all done. you might ask yourself how can i figure out how much money i need if i don't know what i'm gonna be doing in the first place? good question. if you want a carefree trip, bring a lot of money. obviously. but if you're not able to save a lot than i think it would be best to figure out how much the basic stuff is and just double that. if you find out your lifestyle doesn't suit your savings than you know that for your next trip. that's why it's so important to have a credit card with you, just in case and once you're back home you can always just pay it off. the thing about traveling is that you always think that it's a once in a lifetime thing, which will make you not really care about not spending all of your money, because you have to take everything out of it you can, do it all, see it all, live it all. so to budget yourself in a situation like that is very, very difficult. but like so many things about traveling, it depends on who you are and what you want to get out of your trip and how you normally handle money in comparable situations. so think about all of this and make sure you decide something that is right for you, so you won't be disappointed in the end.
basically you have to prepare everything as mentioned in 'preparing A LOT', except for an itinerary.
i like to book the first two nights or so ahead and go from there. talk to people, take a bus to wherever, sleep on people's couches, put yourself completely outside of your comfort zone and experience things you'd never thought would ever happen. and don't forget to eat weird food, you have to eat weird food.
depending on the country, you could for example book a flight to one city and book a flight out of the country from another city and just travel from flight in to flight out. the thing about not having an itinerary though is that you might miss out on certain things that are worth seeing or doing in a certain country, but on the other hand you get to do unprepared stuff. it depends completely on what kind of person you are and what kind of trip you want to do.