First, you have to learn the basics of flutter and dart so you can learn them from the Acadmind course available on Udemy.

Flutter & Dart – The Complete Guide [2021 Edition]

Stage 2:

Now start making some simple apps like News App, Weather App, Quiz App, etc. For this, you can take help from Youtube.

Stage 3:

Now start learning about Bloc(state management) and some intermediate and advanced topics. The best source for this is to learn from the Youtube channel name “Resocoder”.

Stage 4:

Start learning about the architecture in android development by watching these two playlists from Resocder:- TDD and DDD

Now practice the same apps like news app, weather app, quiz app, etc. using the technique which you have learned in stage 3 and stage 4.

Now you are good to start with your apps and making your projects.