Charge as much as you can as often as you can. Way too many people don't charge enough. Be licensed and insured, and prove it. Clients are willing to pay more knowing that you are insured, and are willing to take responsibility for damages that may happen. Carrying a 2 million dollar policy is not that expensive.
Always have a backup plan. For weather delays or malfunctions or if you need to rent or even buy an extra drone. I only own one P4 but plan to buy another. I have only used my drone for two paying jobs. I used a 333 pilot for one of them as I am not certified yet.
Expenses you incur,
Travel and gas
Equipment (drone, batteries, gas, filters)
Editing (software, computer, computer time, upload time, thumb drives, web hosting, file hosting)
Training (107 classes and certification)
Hire a cop if there are crowds...
Be professional, know what you are doing and what to do if something goes wrong.