These are my favourite tips and tricks. These are only those who me and my colleguages have tried out.
Architecture tips
Keep it slim
Functions should do one thing and they should do it well. When you develop it in C# and Visual Studio, it is so tempting to develop a “microservice” in a good way, you add interfaces, implement good patterns, and all of a sudden you get a monolith packaged in a microservice. If your function grows, stop, rethink. Better to see how it input and output bindings can be used. Also orchestration with Logic Apps or Durable Functions can help.