1. You need to understand what problem you want to solve by going serverless. Is it to lower the costs or to replace your legacy code with some parts of new managed service , maybe it's something else?
2. Know your budget - you need to understand how much money you spend on your infrastructure AND your developers right now. And plan how much you can spend on the serverless infrastructure. When planning the last one - keep in mind that you can replace parts of your system that you maintained before - by AWS or any other cloud managed services, so time and money you were spending on maintaining your current system - can be focused on just usinig managed service that will do all the work for you.
3. Change your team mentality - when going into serverless world developers still have tendency to try applying old observability and troubleshooting methods on new system which will lead to disappointment and confusiion, while it should be shift in your team thinking. Ask your developers to spend some time on learning more about serverless, create internal discussions for your team, find some consultant with good experience - so you don't need to go through the full process on your own.