Assuming you have some early stage funding, the most important thing is to focus on building and shipping your product. With that said, you need to be aware of your burn rate (i.e. how much money you're spending each month) and make sure you have a glide path to reaching profitability.
There are a number of ways to track your burn rate, but one simple way is to track your monthly operating expenses (OpEx) and compare it to your monthly revenue. If you're not generating revenue yet, you can track your OpEx as a percentage of your total funding.
To get started, you can use a spreadsheet or budgeting software to track your income and expenses. I like to use Mint because it's free and easy to use. You can also find a number of templates online (just search for "startup budget template").
Once you have a good handle on your monthly burn rate, you can start thinking about ways to reduce it. For example, you might want to renegotiate leases, cut back on marketing spend, or reduce headcount. The key is to focus on reducing your burn rate without sacrificing too much growth.
If you're not sure where to start, I recommend talking to your investors or hiring a financial advisor who specializes in startups. They can help you put together a budget that will allow you to reach your goals.
