Start with a plan. Make sure you know what you are going to do, how you are going to do it, and when it is going to be completed. This will keep you from making the same mistakes that other business owners and founders have made in the past (i.e. over-promising, underestimating, under-spending).
A plan can take many different forms and can be as simple as a spreadsheet with bullet points or simple goal tracking app like Trello or Asana. Whatever method works best for you is fine. The point is to make sure that you have a plan in place that sets out exactly what you are going to do and when you are going to do it.
Once you have your plan in place, get started executing! Start with one small step at a time and work your way up to the bigger picture goals of your business. It is important not to try and do everything all at once. Instead, start with one or 2 things that are manageable and can be completed in a short period of time if necessary. Eventually, your small tasks will lead up to the bigger picture goals of your business.