There are a lot of things that can go wrong when you're trying to manage your own cash flow. It's easy to get overwhelmed by the sheer number of things you have to do, and if you're not careful, it'll be all too easy for the whole thing to fall apart.
But here are a few tips that will help you keep your head above water:
Make a list and check it twice. Before you start spending money, make a list of everything you need as well as everything you want. Then, prioritize by importance (e.g., rent first, then food), and don't forget about any bills that need to be paid on time.
Keep track of what's coming in and out. If possible, try keeping an Excel spreadsheet with all your income and expenses so that it's easier to see where your money is going at any given time.
Always save up some cash for emergencies. You never know when something unexpected might come up.