Since I started working for myself at my coffee shop I had to organize all my expensive, I mean, I need to write down all the things that I buy, everything. I do this for my businesses and also for my day to day life. This way I always keep track of all of my expenses.
I don't use any fancy app or program, I just use Excel and rearrange everything so it looks more "presentable". I like using Excel because it's easy to work with and you can personalise it to your need and taste.
Here is how I organize it:
1. I create categories - this is a easier way for you to keep track of what things are you spending most money on, I like to divide mine in Shopping, Going Out & Dinners and Others.
2. Always write what the expense is - an order from Asos, or a lunch with a friend. Just write it down.
3. Work with even numbers - a dress that cost 12,99€, round it up to 13€. It's easier for the calculations.
I do give myself budgets, but I don't always follow them because I know how to control my shopping, and when I get my own place I will probably have to stick to those budgets, but for now I just enjoy what I can, and I always save a great amount of money each month.