first of all you can’t do anything wrong. You can start with your permanent expenses, these are the ones, that are recurring every month. For example, your rent or telephone bill.
Next step would be if you have debts, to consider them as well.
Then also add a budget for leisure activities. Consider all the fun things you want to do in this month, so your budget can be sustainable. This will make it also easier to stick with your budget.
The thing with budgeting is, that budgets are always changeable. If you recognize after a while, that you need less or more money for a particular category then you can always change it afterwards.
This is also how you can manage to stick with a budget in the long run. It’s no fun at all if you never can stay in your budget, then you soon will feel frustrated and probably stop budgeting. So adjust your budget when it’s needed or check your expenses and when possible adjust them, so you can stick with your budget again.
This blog post might give you additional help and input: https://www.getzuper.com/blogpost/budget-banking-app
Please let me know if this was helpful and if I answered your question