This is a great question and one that is unique to each individual's financial circumstances, goals, and risk tolerance. However, here are some general guidelines:

Emergency Fund: First, ensure you have an emergency fund in place. This is typically 3-6 months of living expenses saved in a liquid account, like a high-yield savings account. This money is not for investing, it's a safety net for unexpected costs like medical emergencies or job loss.

Budgeting: Next, look at your budget. How much money do you have left over after paying for necessities and setting aside money for your emergency fund? A good practice is to aim to invest about 15-20% of your income. But, if that's not possible, remember that any amount counts, and it's better to start small than not start at all.

Goals: Your investment goals will also influence how much you should invest. If you're young and saving for retirement, you might be able to invest a smaller amount and let compound interest do the work over the years. But if you're older and playing catch-up, or if you have a shorter-term goal, like buying a house in five years, you might need to invest more.

Debt: If you have high-interest debt, like credit cards, it might be wiser to pay that off before investing heavily, as the interest you're paying could negate your investment returns.

Let's say, for example, you're Jane, a 30-year-old with a monthly income of $4000. You spend $2500 on necessities and have $1500 left. You already have an emergency fund in place. You might decide to invest 20% of your income, which would be $800 a month. If you still have high-interest debts, you could use part of the remaining $700 to pay those off more quickly.

This is a simplified example, and you'd need to adjust it for your situation. It's a good idea to speak with a financial advisor to create a plan tailored to your needs. Always remember: the key is to start investing as soon as you can, even if the amount seems small. Small, regular investments can add up over time due to the power of compounding.