First of all, I want to congratulate you for actually deciding to travel even though your budget may be (really) limited. That takes a huge pair of balls.
Second, I want to help you squeeze every bit of fun you possibly can out of the money you have, because otherwise what is the point in spending it? There are a few things you should probably do in order to really maximize your time and budget, but of course I am not an expert, and these are just things that have worked for me.
One of the best ways you can stick to a budget is to research your brains out.
And I mean like, summon your inner scientist or graduate school student and really take the time to delve into each place that you want to visit and understand what you are going to be expected to spend for different things. Not only will this help you plan accordingly, but it will help you decide what is the most important to you during a trip and allow you to focus your funds on that thing, rather than randomly and impulsively spending your money along the way.
Researching the prices of a place and costs of actives also helps you cut spending in areas you don't need to break the bank on. For example, if you are in Costa Rica and you decide you really want to go zip lining, you can save money in other ways by buying food at grocery stores instead of eating out at every meal. Or, if you are in Italy and you desperately want to go to Pompeii but didn't realize how much it would cost, you can plan on not going out drinking while your there, which is probably the quickest way to accidentally spend all of your money in one place.
Be willing to give up some of your "creature comforts".
Traveling cheaply is often going to mean giving up the fancy hotels with the luxury spa and room service, obviously. But it can also mean going even below a budget hotel by staying in a crowded hostel dorm or even camping, if the weather allows for it. It can mean being willing to not shower very often or shower in cold water or maybe water that has very little water pressure. I vividly remembering showering under a cold hose in a shack in Costa Rica with a tampon (not mine) by the drain and a line of ants running along the wall. While I didn't appreciate the 5 minutes a day I had to spend in the shower, the other 1,435 glorious minutes of the day were totally worth the sucky living situation.
To take it a step further, trying doing a work exchange.
Basically, this means you would be voluntarily working for someone for a certain number of hours in exchange for a free place to stay, and often times free meals are included as well. A great site I have used to find a work exchange is workaway.info. I traveled through Latin America using this site and volunteered at a surf camp in Costa Rica, a hotel in Nicaragua, and a horse ranch in Mexico, to name a few. Some places I worked as little as 1-2 hours a day, and other places I worked up to 5 hours a day. More often than not, I also got 1-3 free meals! The only drawback with doing a work exchange is many hosts have a minimum stay requirement, to make it worth their time, so it is really only something you can use if you have 2 weeks or more to spare. But this essentially means your budget would only have to include money for your flights, activities, and the occasional meal. Not to mention you get to meet new people, interact with locals, and create an incredibly unique experience you would never find in an Airbnb or a hotel.
Don't forget to be mindful of how you are eating and drinking.
This has nothing to do with your health, but everything to do with cash. It is soooo easy to drop a ton of money on eating out when you're traveling. Trust me, I know. Food is my life. But spending $10 a day on food versus spending $30 a day on food adds up quickly when you're traveling for a week or longer. If you are staying somewhere with a kitchen, and the majority of hostels have a community kitchen available for your use, take advantage of it and cook cheap meals for yourself. Or better yet, split it with another person. And don't forget to pass up on the free breakfast offered, even if it isn't exactly a 5-star meal.
Also, stop buying plastic water bottles! Not only is it bad for the environment, but it is bad for your wallet. (This rule is waved if you are in a country that does not have easy access to potable drinking water.) Just bring your own water bottle, fill it up whenever possible, and use the $6 a day you are saving on bed in a hostel in Nicaragua.
And I know part of the fun of being in a new country is going out at night which often includes alcohol. And I won't tell you to stop doing that. But maybe, save it for one or two nights. Not only will you have more energy the next day to explore the new place you are in, but considering drinks can cost upwards of $6 at a down-scale place, you will also save a crazy amount of money. And you don't need me here to tell you that the drunker you get, the more likely you will spend even more money on drinks and then take everyone out to eat junk food afterwards. You can do that in your home country.
But don't forget to treat yourself to at least one traditional or cultural meal of the place your visiting, because a new experience with new food is an adventure in and of itself.
Use public transportation whenever possible and be willing to take the longer route.
I know it can be so much more convenient and sometimes faster to take a taxi or an Uber, but public transportation is going to cost you a fraction of what a personal service or car rental would. Even in places that don't have super strong public transportation systems in place, like Central America or South America, they will almost always have some sort of bus system in place, even if it is fairly unreliable or not super punctual. I traveled from Costa Rica to Nicaragua using a public bus, and it took a total of 10 hours because I had to make a transfer and the bus had to make a stop so the driver could have a coffee break, but it cost me $10 dollars, while using a shared shuttle service would have cost me 5 times that amount. This is where you have to be willing to be a little bit patient, throw your sense of personal space out the window, and enjoy the scenery. But not only will it save you money, but it will be a whole other adventure and you will get to see parts of the country so many will not.