First rule of contractor life, keep your business and personal finances separate to avoid commingled funds and mass confusion at year end.
If you’ve set up a limited company, this could help as you would typically have an associated business bank account and accounting software to help you stay on track. If not, explore what the pros and cons might be for your personal situation. Either way, do your research on the best business accounts available, set up book-keeping software like Xero or Quickbooks to manage your invoicing and keep your receipts. Most apps enable you to upload pictures of paper receipts to eliminate the messy and unreliable paper trail of yesteryear.